Endversion1 skriptum characterization of miscellaneous multi parametrical silicon based biosensor chips

Table of contents

Table of contents

Table of contents .................................................................................................................. 1
1 Introduction .................................................................................................................. 4
2 Materials and methods.............................................................................................. 7
2.1 Microscopes..................................................................................................................... 7
2.1.1 Purpose of use ............................................................................................................................................ 8
2.1.2 Used equipment and items ................................................................................................................... 8
2.1.3 Available settings...................................................................................................................................... 8
2.2 Used PC software ........................................................................................................... 9
2.3 Phosphate-Buffered Saline (PBS) .......................................................................... 11
2.4 Ag/AgCl reference electrode ................................................................................... 12
2.4.1 Purpose of use ......................................................................................................................................... 12
2.4.2 Used equipment and items for production ................................................................................ 13
2.4.3 Producing assembly ............................................................................................................................. 14
2.4.4 Production procedure ......................................................................................................................... 15
2.5 Incubator ........................................................................................................................ 17
2.5.1 Purpose of use ......................................................................................................................................... 17
2.5.2 Available settings................................................................................................................................... 18
2.6 Regulated DC power supply unit ........................................................................... 19
2.6.1 Purpose of use ......................................................................................................................................... 19
2.7 Voltalab® 80/10 .......................................................................................................... 21
2.7.1 Purpose of use ......................................................................................................................................... 21
2.8 Sensor chips .................................................................................................................. 26
2.8.1 cMOS ............................................................................................................................................................ 27
2.8.2 nMOS ........................................................................................................................................................... 30
2.9 Pin box ............................................................................................................................. 34
2.9.1 Purpose of use ......................................................................................................................................... 34
2.9.2 Available connectors ............................................................................................................................ 35
2.10 Non-Semiconductor sensors ................................................................................... 38
2.10.1 Clark sensor (Amperometry) ........................................................................................................... 38
2.10.1.1 Idea ................................................................................................................................................... 38
2.10.1.2 Equipment and items ............................................................................................................... 41
2.10.1.3 Measurement assembly .......................................................................................................... 43
2.10.1.4 Measurement settings and parameters ........................................................................... 44

Characterization of miscellaneous multi parametrical silicon based biosensor chips -1-

Table of contents

2.10.1.5 Procedure ...................................................................................................................................... 45
2.10.2 IDES Sensor (Impedimetric) ............................................................................................................. 46
2.10.2.1 Idea ................................................................................................................................................... 46
2.10.2.5 Procedure ...................................................................................................................................... 51
2.11 Semiconductor sensors ............................................................................................. 52
2.11.1 Temperature Diode (Potentiometry) ........................................................................................... 52
2.11.1.1 Idea ................................................................................................................................................... 52
2.11.1.5 Procedure ...................................................................................................................................... 56
2.11.2 Reference MISFET (nMOS) ................................................................................................................ 57
2.11.2.1 Idea ................................................................................................................................................... 57
2.11.2.5 Procedure ...................................................................................................................................... 61
2.11.3 ISFET Sensors for pH-Measurement ............................................................................................. 62
2.11.3.1 Idea ................................................................................................................................................... 62
2.11.3.5 Procedure ...................................................................................................................................... 66
2.11.4 O2-FET Sensors for DO-Measurement .......................................................................................... 67
2.11.4.1 Idea ................................................................................................................................................... 67
2.11.4.5 Procedure ...................................................................................................................................... 73
2.11.5 CV-FET (an extended O2-FET Sensor) .......................................................................................... 74
2.11.5.1 Idea ................................................................................................................................................... 74
2.11.5.3 Procedure ...................................................................................................................................... 75
3 Results and Discussion ........................................................................................... 77
3.1 Non-Semiconductor sensors ................................................................................... 77
3.1.1 Clark sensor ............................................................................................................................................. 77
3.1.1.1 cMOS chips .................................................................................................................................... 78
3.1.1.2 nMOS chips ................................................................................................................................... 79
3.1.2 IDES Sensor .............................................................................................................................................. 80
3.1.2.1 cMOS chips .................................................................................................................................... 80
3.1.2.2 nMOS chips ................................................................................................................................... 80
3.2 Semiconductor sensors ............................................................................................. 82
3.2.1 Temperature Diode .............................................................................................................................. 82
3.2.1.1 cMOS chips .................................................................................................................................... 82
3.2.1.2 nMOS chips ................................................................................................................................... 83

-2- Characterization of miscellaneous multi parametrical silicon based biosensor
chips

Table of contents

3.2.2 Reference MOSFET (nMOS) .............................................................................................................. 85
3.2.3 ISFET Sensor ............................................................................................................................................ 86
3.2.3.1 cMOS chips .................................................................................................................................... 86
3.2.3.2 nMOS chips ................................................................................................................................... 87
3.2.4 O2-FET Sensor ......................................................................................................................................... 90
3.2.4.1 cMOS chips .................................................................................................................................... 90
3.2.4.2 nMOS chips ................................................................................................................................... 91
3.2.5 CV-FET Sensor (nMOS) ....................................................................................................................... 93
4 Problems and Solutions ......................................................................................... 99
4.1 Contacting errors ........................................................................................................ 99
4.2 Loosing of the passivation layer ......................................................................... 100
4.3 Noise.............................................................................................................................. 103
4.4 Signal drops while measuring ............................................................................. 104
4.5 Digital rounding errors .......................................................................................... 104
4.6 Unclean sensor surface .......................................................................................... 105
5 Conclusions and outlook ...................................................................................... 106
6 Acknowledgments .................................................................................................. 109
7 Indexes....................................................................................................................... 110
7.1 Index of pictures ....................................................................................................... 110
7.2 Index of graphs.......................................................................................................... 111
7.3 Index of equations.................................................................................................... 112
7.4 Index of tables ........................................................................................................... 112
8 List of abbreviations and symbols .................................................................... 114
9 Bibliography ............................................................................................................ 119
10 Appendix ............................................................................................................... 123


Introduction

1 Introduction

The biomedical analysis techniques require the development of smart sensors
with the following properties: mass fabrication, low cost, low power and ease of
use. In this goal, various sensors have been developed to cover the needs of the
biomedical researches. In these researches, biological cell cultures are analyzed
under different conditions. The biochemical activities of these cultures change
some parameters of the environment which they live in. This environment can be
enclosed and protected from any outer effects, so any changes by the living
biological cells can be detected using various detecting methods. One of these
methods is the electrochemistry, which is the detecting of electrical signals
caused by chemical reaction.

An electrochemical cell is a chemically and electrically isolated environment.
Therefore the isolated environment, which the biological cells live in, can be
handled as an electrochemical cell.

Electrochemical cell. Picture 1-1

-4- Characterization of miscellaneous multi parametrical silicon based biosensor chips

Introduction

There are three basic electrochemical cell processes that are useful in
transducers for sensor applications:

1. Potentiometry, the measurement of a cell potential at zero current.

2. Voltammetry and analogue amperometry, in which an oxidizing potential
is applied between the cell electrodes and the cell current is measured.

3. Conductometry, where the conductance and resistance of the cell is
measured by an alternating current bridge method.

Semiconductor sensors have the advantage that they have smaller dimensions
then other materials and several sensor types can be easily integrated in one
chip. Electronic miniature circuits and structures e.g. memory or amplifier can
produced in the same wafer with the sensor at the same time. On the other hand,
only mass produced semiconductor sensors are economically producible.
Alternatively, researches are also done using thin film technology to produce
sensors on glass or ceramic. This is cheaper and easier.

Because the rapid development the semiconductor production and the high
quality at small dimensions, the silicon sensors are not to disregard. Therefore
the Lehrstuhl für medizinische Elekronik – the Chair for medical electronics- at
Technische Universität München has developed silicon sensor chips to monitor
the activity of living cell.

The most important parameters to measure are oxygen concentration and pH
value under monitoring temperature and adhesion.

Parameter Silicon Thin film
[MICH06] technology technology
Temperature pn diode Pt1000
Dissolved Clark Sensor
Clark Sensor
oxygen O2-FET
pH ISFET Metal oxide

Used sensors on silicon and thin film technologies. Table 1-1

For the pH measurement, the ion-sensitive field effect transistor (ISFET) was
used. It provides all the requested advantages and its potentiometric principle is
well adapted to the detection of ions for pH value. Thus, many researches to
increase the pH sensitivity were done for the development of ISFETs.


Introduction

Because the ISFETs were only for measuring pH it was not able to detect
dissolved oxygen in the electrolyte fluid without disturbing it with other
substances to cause a chemical reaction resulting in change of pH value. It was
not possible to limit this chemical reaction to be locally, so the same fluid can be
used again. A solution for this problem was to use electrochemical half reactions,
which can be controlled very locally and without the need to add other
substances. The electrochemical half reactions can be produced by applying a
potential at an electrode, which is small enough to keep the reaction locally. The
produced ions are only in the surrounding area but in the same time they are
enough to produce an electrical potential to be detected by the ISFET sensor.

For this an O2-FET was developed and evaluated successfully. The work idea for
O2-FET was also to be generalized to measure other dissolved materials than
oxygen. This requires the improvement of the O2-FET measurement procedures
from a pulse operating mode to a cyclovoltammetrical scan mode, so the
measured values are significant to concentration of substances we want to
detect.

In addition to O2-FET, a Clark type sensor -which is also on the same chip-, can be
used for measuring dissolved oxygen and confirm the results of the O2-FET.

The main work points in this assay are:

1. Examine the sensor chips of visible production errors.

2. Investigating available measurement methods.

3. Theoretical explanation of the measuring methods.

4. Construction of measurement system for each sensor.

5. Procedure of measurements.

6. Discussion of the measured data.

7. Determination of malfunction and failure sources.

8. Development and improvement the measurement procedures.


Materials and methods

2 Materials and methods

In this chapter the used materials for the characterization of the sensor chips are
presented. Recommended working steps and available setting of the used
equipment are also described.

2.1 Microscopes

The used microscopes with digital cameras. Picture 2-1



2.1.1 Purpose of use

To examine the sensor chips optically for visual manufacturing errors before the
beginning of the evaluating.

Comparing the pictures of the sensors before and after measuring will give lot of
information about its aging process and it is opportunity to specify common
errors of the chips.

2.1.2 Used equipment and items

DIGITAL CAMERAS:

Nikon E4300: Was used to take the pictures using the first microscope
with the high magnification factor.

Nikon E5400: It was connected to the second microscope.

CARD READER:

To transfer the photos taken by the camera from the memory card, where
the cameras save the photo files, to a PC using the USB port.

2.1.3 Available settings

The pictures were taken with the digital cameras. The digital camera was
connected to the microscope by an optical adapter with lens. Additional the
optical zoom of the camera is also used. An accurate zoom factor therefore
cannot be given.

The first microscope has a bigger zoom factor and it can only magnify the
individual sensors on the chip. The second microscope cannot magnify as good
as the first one, but it used for taking pictures of the whole chip surface.



2.2 Used PC software

ORIGIN PRO 8:

It is a professional data analysis and graphing software for engineers. It
can handle huge amount of data more efficient than other programs. Its
multi-sheet workbooks, publication-quality graphics, and standardized
analysis tools provide a tightly integrated workspace to import data,
create and annotate graphs, explore and analyze data, and publish work.

VOLAMASTER 4 V7.08:

It is software with an easy configurable measurement sequence editor for
the Voltalab measuring unit. It gives the possibility to monitor the
detected response signal in real time and record these values in data
tables. The program VoltaMaster 4 has also the ability to show the
captured data in graphs, apply filters, and change parameters to highlight
information.

MS WORD 2007:

A good known word processing software. The version 2007 uses a new
file format called docx. Word 2000-2003 users on Windows systems can
install a free add-on called the "Microsoft Office Compatibility Pack" to be
able to open, edit, and save the new Word 2007 files. Alternatively, Word
2007 can save to the old doc format of Word 97-2003 and edit it, but then
is not possible to use the “Equation Editor” any more.

MS PAINT:

A simple graphics painting program that has been included with almost
all versions of MS Windows. The used Windows version is Vista, which
has more undo levels and better crop functions. The main improvement is
to add zoom slider, which increased the work speed with small objects.
The program can edit and save in the most known non layer graphic file
formats.



MS POWERPOINT 2007:

To make a presentation of this work with figures and animations.

ADOBE ILLUSTRATOR CS3:

Used to design some figures in vector graphics format.

MS EXCEL XP/2007:

To plot the raw data of the acquired measurements in graphs and
diagrams.

MATHTYPE 6.0:

A plug-in for MS Office package as an alternative to the Equation Editor
which comes with MS Office.

ADOBE ACROBAT PROFESSIONAL 8:

To make a PDF version of this electronic document for the publication.
Files in PDF format are platform independent and contain the fonts used
in the document.

MS VISIO 2007:

Used to design some figures in vector graphics format, it contains also a
graphic library to use in making data flow diagrams and work plans.

- 10 - Characterization of miscellaneous multi parametrical silicon based biosensor chips


2.3 Phosphate-Buffered Saline (PBS)

PBS solution is used widely in biochemistry and biological research. That’s
because its osmolarity and ion concentration usually match those of the human
body, and because it maintains a constant pH value.

=
ℎ

Molarity Equation. Equation 2-1

Components Mole Weight Concentration Molarity
[MICH06] (g/mol) (g/l) (mM)
KH2PO4 136 0.20 1.47
NaCl 58.5 8.00 138
Na2HPO4 * 2H2O 178 1.44 8.1
KCl 74.6 0.20 2.68

PBS buffer composition. Table 2-1

The PBS solution used has a pH value of about 7.15.

BONDING DISSOLVED OXYGEN

In addition, to bond from air dissolved oxygen molecules in the PBS it is enough
to add 10g sodium sulfite Na2SO3 to 1l PBS. For an accurate measurement this
solution must be used fresh. The resulted PBS has a pH value of about 8.10.

Substance Mole Weight Concentration Molarity
[GEST08] (g/mol) (g/l) (mM)
Na2SO3 126 10.00 79.4

Used sodium sulfite concentration for bonding dissolved oxygen. Table 2-2

Characterization of miscellaneous multi parametrical silicon based biosensor chips - 11 -


MORE FREE IONS

To make solutions with more dissolved free ions than 150mM of NaCl, we add
8.8g to one liter PBS to double the molarity to 300mM. To make several
concentrations it is easier to dilute a higher concentrated solution with PBS. For
concentrations below molarity of a usual PBS we add deionised water.

Substance Mole Weight Concentration Molarity
[MICH06] (g/mol) (g/l) (mM)
NaCl 58.5 16.80 288

Concentration of the NaCl to double the amount of the free ions. Table 2-3

2.4 Ag/AgCl reference electrode

Reference electrode is an electrode which has a stable and known potential. The
stability of the electrode potential is reached by employing a redox system with
constant concentrations.


Reference electrodes are used to keep the electrolyte at a constant potential,
without causing electrical current to flow within the electrolyte. The reference
electrode is difficult to build on the silicon chip by using integrated circuit
technology. That is because a reference electrode uses an electro chemical
reaction to move ions from an electrode into solution.

A silver/silver chloride wire is used as reference electrode due these features:

- Stable standard potential of 0.2V [MACA78].
- Non-toxic components.
- Simple construction.
- Inexpensive to manufacture.



The motion of chloride ions at Ag/AgCl wire causes current, which can be

e- + AgCl ↔ Ag + Cl-
explained as [FARM98]:

Reference electrode current. Equation 2-2

The corresponding Nernst equation for this reaction is:

= − ln [ ]

The voltage of reference electrode. Equation 2-3

To avoid current to flow through the electrode and then to the electrolyte, a 3M
KCl solution is used.

2.4.2 Used equipment and items for production

VOLTALAB:(PULSE-CHRONO POTENTIOMETRY)
The current that will flow though the electrolyte is set to constant value.
The corresponding voltage is also recorded.

SILVER AG WIRE:
Cut in handy 4cm peaces wire.

PLATINUM PT WIRE:
One peace 4cm wire.

HYDROCHLORIC ACID HCL SOLUTION:
With a molarity of 0.1M.



2.4.3 Producing assembly

Electrolysis by electrochemical oxidation of the silver wire in 0.1mM
hydrochloric acid HCl solution:

- Ag as anode at the plus pole (Work-Prot) of the voltage source Voltalab.
- Pt as cathode at the minus pole (Ref-Port) of Voltalab.

Wiring schema for the production of Ag/AgCl electrode. Picture 2-2

While producing an AgCl on the Ag wire the following chemical reactions
happen:

On the Ag-Anode side:

2Ag + 2 HCl à 2 AgCl + 2 H+ + 2 e- (AgCl is darker than Ag)

Half reaction the Ag side. Equation 2-4

On the Pt-Cathode side:

2 H + + 2 e- à H 2 (H2 bubbles rise on Pt)

Half reaction the Pt side. Equation 2-5



So the whole reaction can be summed to:

2 Ag + HCl à 2 AgCl + H2

The whole chemical reaction for producing Ag/AgCl electrode. Equation 2-6

2.4.4 Production procedure

1. A constant current of 4mA to flow through the electrodes is applied

2. Becoming the silver wire darker and rising hydrogen gas on the platinum
wire is an indicator for building silver chloride.

0 50 100
Time [s] 150 200 250
-0,7

-0,8

-0,9

-1

-1,1
Voltage [V]

-1,2

-1,3

-1,4

-1,5

-1,6

-1,7

The measured electrolysis voltage at 4mA for producing Ag/AgCl. Graph 2-1

3. After few minutes (4 minutes) the hydrogen bubbles will stop to develop
on the platinum side, this means the silver chloride is already reached its
maximal thickness on the silver wire.



Electrolysis current for producing Ag/AgCl. Graph 2-2

This period can be also known from the electrolysis current curve below, where
the current a 1mA doesn’t change anymore, if we applied a constant voltage
instead of current.



2.5 Incubator

The used incubator. Picture 2-3

The used incubator is Kelvitron t6030 from Heraeus Instruments. It has a
volume of 30l and offers enough space to set the sensors and its pin box, without
having an unneeded free volume to heat. The more volume there is to heat the
more time is needed to reach the target temperature.


To make and keep a constant tempered environment for temperature dependent
measurements.



The incubator can be also used as faraday cage.


The incubator can heat up to 300°C. Therefore, it is not possible to have a
temperature below environment temperature in the room. Although, it accepts
settings below room temperature, but this practically cannot be realized. Cooling
down takes several hours. So, when measuring at many temperatures, it is easier
and faster to begin with the lowest temperature.

Damped oscillations of the incubator. Graph 2-3

Heating up the air in the incubator to a constant target temperature needs
relatively long time compared e.g. to a fan oven. This is because the oscillation of
the heating process of the incubator, which uses pulsed operating of the heating
elements without circulating the air. The bigger the difference between target
and start temperatures is, the bigger is the oscillation amplitude and time to get a
constant target temperature.



2.6 Regulated DC power supply unit

The used Power supply [CONR08]. Picture 2-4

Laboratory power supply VLP-1303 PRO delivers constant potential difference
between its input minus port and output plus port. The potential difference can
be adjusted manually and displayed with its corresponding current flowing
through the ports.

The voltmeter is used to control the adjusted voltage. The display of the power
supply has not enough digits to display the applied voltage exactly. The display
can have here a rounding error up to 100%, because the missing second and
third digit after the radix point, which can be 99, a voltage of 0.099V can be
shown inaccurate on the units display as “00.0V”.


The voltage supplied by this unit is used to raise the potential of the gate above
the source potential on the reference MOSFET of nMOS chips. This potential
builds the electrons channel between source and drain. Through this channel can
current flow. The width of this channel is controlled by the applied voltage at
gate using this power supply. This voltage must be very constant; otherwise the
small changes of this voltage can affect the transistor current very much, so the
characterization cannot be done as desired.




The power supply has two outputs. The first output has a range of 0V to 3V at a
maximal current of 3A. The second output has a range of 3V to 6V at maximal
current of 2A.

The unit -beside the supplying of a constant voltage- can also limit the current
flow through the first output. To do that; turn the control AMPERE clockwise
until the red LED for current limiting (CC or OL) referring to the output goes off
and the green LED for voltage limiting (CV) lights up. Then the VOLT control can
be used to adjust the desired output voltage.

It is not possible to limit current at the second output, that’s why it has only one
control to adjust. By using the pushbutton, the voltage of the second output can
be displayed. Simply, hold the button down as long as is wished to see the values
on the display.



2.7 Voltalab® 80/10

Measurement unit PGZ402 [RADI68]. Picture 2-5


VoltaLab 80 and its basic version VoltaLab 10 are simple and easy to configure
potentiostats PGZ402/100 and electrochemical software VoltaMaster 4
combinations, for recording, analyzing and evaluating of electronic and
electrochemical elements. The VoltaLab unit is connected to a PC via the RS232
interface port.


Voltalab has the software GUI VoltaMaster 4. VoltaMaster 4 v7.08 is an easy
configurable measurement sequence editor. It gives the possibility to monitor
the detected response signal in real time and record these values in data tables. It
has a huge amount of possible configuration settings to measure and evaluate
circuits connected to the system. Voltammetry, amperometry and coulometry
are only some examples of the methods, which Voltalab can be used for.

The program VoltaMaster 4 has also the ability to show the captured data in
graphs, apply filters, and change parameters to highlight information.



GUI interface of the VoltaMaster 4. Picture 2-6

Some technical data of PGZ402 [RADI68]:

Specifications Working range
Maximum compliance voltage ±30V
Maximum current output ±1A
Maximum polarisation voltage ±15V
A/D converter 16bit
Measurement period 500ms
Max. scan rate 20V/s
Max. frequency 100kHz
Min. frequency 1mHz
Dynamic Impedance Driven up to 100mV/s
Static manual & Static auto up to 1V/s
Feedback manual & Feedback auto up to 20V/s

Specifications cable of the PGZ402. Table 2-4

The next graph shows an example measurement at a 10MΩ resistor. For this
measurement one side of the resistor is connected to the WORK-input of the
PGZ402 and the other side is connected to the REF- and the AUX-input. The



voltage-current V-I curve is absolutely linear and there are no visible jumps
between the measurement ranges. [WIES03]

Measurement of a 10MW resistor with the PGZ402 unit. Graph 2-4

OPEN CIRCUIT POTENTIAL:

The Open Circuit Potential corresponds to the WORK potential measured
versus the REF potential. As the name of the measurement method
implies the circuit is open so there is no current to flow and measure. A
measuring sequence of 30 seconds is enough to calibrate to a drift
threshold near zero.

Available settings for Open Circuit Potential measuring method. Picture 2-7



POT. CYCLIC VOLTAMMETRY

Cyclic voltammetry sweep the potential at a given rate and measure the
current. The curve obtained is known as a "voltammogram", where
voltage to current values are plotted. A ranging for current measurement
is available depending on the scan rate.

Available settings for Pot. Cyclic Voltammetry measuring method. Picture 2-8

PULSE - CHRONO POTENTIOMETRY

The WORK potential is measured versus the REF potential while the
current is maintained at a pre-set value.

Available settings for Chrono Potentiometry measuring method. Picture 2-9



PULSE - CHRONO AMEPEROMETRY

The current flowing from REF to WORK is measured while the potential
between them maintained at a pre-set value.

Available settings for Chrono Ameperometry measuring method. Picture 2-10

IMPEDANCE - POT. FIXED FREQ. EIS (CAPACITANCE)

The WORK potential versus REF is imposed and the electrochemical
impedance is recorded at one fixed frequency with an AC signal. A real
time plot displays Zimaginary and Zreal versus potential.

Available settings for Pot. Fixed Freq. EIS (Capacitance) measuring method. Picture 2-11



2.8 Sensor chips

In this assay, we have two kinds of chips to probe. Both chips have the same kind
of sensors, which are temperature, Clark, IDES, ISFET and O2-FET sensors.

The first produced chip lot was manufactured at Micronas AG. We refer to this lot
with the name cMOS. The second was produced at the Lehrstuhl für Medizinische
Elektronik and we name it nMOS. Although both chips are in cMOS technology
and in nMOS channel structure, we select this notation from its development
history.

At the early stages, sensors were made on glass chips, and then came out the
silicon cMOS compatible production technology, and with the next design, it has
been more specifically so it is called nMOS referring to the n channel structure on
a p-substrate. It is not to mix up with the cMOS and nMOS pair, where it refers to
digital circuit design.

The following short compression can be useful to know more about the
components on the both sensor chips:

cMOS nMOS
d=6mm
Chip reservoir A=28mm²
V=7µL
68 contacts
Chip board
A=24x24mm²
Die area A=12.5x14.5mm² A=7.5x7.5mm²
TD 1
CLARK d=35µm
(Work electrode) A=960µm²
IDES A=~3mm² A=10.2mm²
3x (+4x O2-FETs) 4x (+2x O2-FETs)
ISFET
AGate=100x3µm² AGate=100x10µm²
4x 2x
CV/O2-FET
ANME=2096µm² ANME=2600µm²
REF-FET not available 1x

Fast compare between cMOS and nMOS chips. Table 2-5



2.8.1 cMOS

1mm

The cMOS chip and its sensors. Picture 2-12

The cMOS chips have the following objects:

a. Temperature sensor: Using a temperature diode (TD).
b. Adhesion sensor: One IDES with a contact area of about 3mm².
c. Electrode: Metal electrode made of palladium.
d. pH value sensors: 7 ISFET sensors including the sensors of 4 O2-FETs.
e. Dissolved oxygen sensors: 5 Clark type sensors and 4 O2-FET sensors.

The used sensor chips for this project have the names u01, u02 and u03. All are
from the same batch and were examined under microscope for visual noticeable
production errors on the chip surface before beginning of the measurements.

The examination under microscope is repeated casually to prevent any
measurements may interpreted mistakenly and falsify the results.



Pins assignment (not true to size). Picture 2-13

PIN Chip cMOS Connector
1 ISFET A Drain
2 O2/CV-
-FET A Source
3 Drain
ISFET B
4 Source
5 Cathode
Temperature diode
6 Anode
7 Drain
ISFET C
8 Source
9 ISFET D Drain

- 28 - Characterization of miscellaneous multi parametrical silicon based bios
biosensor chips


10 Source
11 Substrate x1 Sub x1
15 Source
ISFET E
16 NME
O2/CV-FET 1
18 Drain
ISFET F
17 Drain
O2/CV-FET F
20 Working electrode
22 Clark sensor Auxiliary electrode
24 Reference electrode
ISFET F
23 NME
O2/CV-FET F
26 Clark sensor 2 Auxiliary electrode
28 Anode
29 Anode 2
IDES
31 Cathode
32 Cathode 2
ISFET F
30 Source
O2/CV-FET F
33 Auxiliary electrode
34 Clark sensor 3 Working electrode
36 Substrate x2
51 Clark sensor 4 Reference electrode
52 Substrate x4
Clark sensor 5



56 NME
ISFET G
58 Source
O2/CV-FET G
59 Drain
ISFET A
60 NME
O2/CV-FET A

Pins assignment of the pin box. Table 2-6

Pin numbers within yellow colored cells means that numbered pin, which
belongs to a sensor, does not exist on the pin box output. (See “Pin box” chapter
2.9 on page 34)

2.8.2 nMOS

1mm

The nMOS chip and its sensors. Picture 2-14



The nMOS chips have the following objects:

a. Temperature sensor: Using a temperature diode (TD).
b. Adhesion sensor: One big IDES with a contact area of about 10mm².
c. pH value sensors: 6 ISFET sensors including the sensors of 2 O2-FETs.
d. Dissolved oxygen sensors: A single Clark type sensor and 2 O2-FET
sensors.

The used sensor chips for this project have the names f5, f8, i5 and c10. All are
from the same batch and were examined under microscope for visual noticeable
production errors on the chip surface before beginning with the measurements.

The letter in the name of the sensor chip corresponds to the horizontal placing
the sensor chip on the wafer, and the number after it is for the vertical place.

The sensor chips on the nMOS 4 inch wafer. Picture 2-15

The examination under microscope is repeated casually to prevent any
measurements may interpreted mistakenly and falsify the results.



Pins assignment (not true to size)[WIES05]. Picture 2-16

PIN Chip nMOS Connector
1 Drain
ISFET A
2 Source
3 Drain
ISFET B
4 Source
5 Cathode
Temperature diode
6 Anode
7 Drain
ISFET C
8 Source
9 Drain
ISFET D
10 Source
15 ISFET E Source



16 O2/CV-FET 1 NME
18 Drain
22 Clark sensor Auxiliary electrode
28 Anode
29 Anode 2
IDES
31 Cathode
32 Cathode 2
63 Drain
ISFET E
64 NME
O2/CV-FET 2
65 Source
66 Drain
67 REF-MISFET Gate
68 Source

Pins assignment of the cMOS chips. Table 2-7

ISFET E has no contact pin for its source contact on the pin box output. Therefore
it is colored in the table with yellow.



2.9 Pin box

Picture of the used pin box. Picture 2-17


The pin box is an adaptor, which converts the contact pins from the base of the
sensor chip board using a PLCC68 socket to BNC connector type. The BNC is an
isolated connector type used widely by most of measuring units in labs. The case
has ports for 48 lines including a connector for the grounding of the aluminum
case.

Although the PLCC68 socket has 68 contacts, which is more than the available
outputs connector on the pin box, there is no need to have all the 68 pins of the
socket to have BNC outputs. That’s because the sensors on the chip need only a
maximum of 46 lines to operate.



2.9.2 Available connectors

PIN Chip cMOS Chip nMOS Connector
1 ISFET A Drain
ISFET A
2 O2/CV-FET A Source
3 Drain
ISFET B ISFET B
4 Source
5 Cathode
Temperature diode Temperature diode
6 Anode
7 Drain
ISFET C ISFET C
8 Source
9 Drain
ISFET D ISFET D
10 Source
11 Substrate x1 Substrate x1 Sub x1
13
14
15 Source
ISFET E ISFET E
16 NME
O2/CV-FET 1 O2/CV-FET 1
18 Drain
ISFET F
17 Drain
O2/CV-FET F
19
22 Clark sensor Clark sensor Auxiliary electrode
21
ISFET F
23 NME
O2/CV-FET F
Clark sensor 2



28 Anode
29 Anode 2
IDES IDES
31 Cathode
32 Cathode 2
ISFET F
30 Source
O2/CV-FET F
34 Clark sensor 3 Working electrode
36 Substrate x2
39
40
41
42
43
44
45
46
47
48
49
51 Clark sensor 4 Reference electrode
52 Substrate x4
Clark sensor 5



56 NME
ISFET G
58 Source
O2/CV-FET G
59 Drain
ISFET A
60 NME
O2/CV-FET A
61
62
63 Drain
ISFET E
64 NME
O2/CV-FET 2
65 Source
66 Drain
67 REF-MISFET Gate
68 Source
grounding

Pins assignment of the nMOS chips. Table 2-8

Pin numbers within yellow colored cells means that numbered pin does not exist
on the pin box output. Empty yellow cells are pins which does not have
corresponding sensor on the chip.



2.10 Non-Semiconductor sensors

Non-Semiconductor sensors are the ones which are on the surface of the chip
and have no contact with the silicon semiconductor layer. Clark and IDES sensors
are produced by silicon technology using metallization and oxidation, but they
are isolated with an oxide layer from the silicon.

2.10.1 Clark sensor (Amperometry)

2.10.1.1 Idea

Voltammogram is applying a voltage ramp to an electrolyte to determine a
voltage region where voltage is essentially independent of current.

A typical voltammogram of aqueous solutions e.g. PBS in range of 0 to -1.4V has
several regions. These regions vary according to dissolves substances in the
solution. The regions of a solution, which is with oxygen dissolved, can be
illustrated and explained as fallowing. [BRIS06]

Typical voltammogram of Clark sensor. Graph 2-5



REGION I (ZERO CURRENT REGION):

The voltage U is not enough to reduce molecules at the work electrode.
The current there is almost zero.

REGION II (INTERMEDIATE REGION):

The ability of the oxygen molecules to pass the electrochemical double
layer (inner and outer Helmholz plane) to the work electrode limits the
current.

Cause of diffuse current of dissolved oxygen [ISRA07]. Picture 2-18

REGION III (PLATEAU REGION):

Transport of oxygen molecules to the work electrode is causing a

electrolyte solution. ∝
diffusion current, which is relative to the concentration of oxygen in the
. This is limited to current.

The width of the region is dependent on the diffusion of the oxygen
molecules. This can be explained with Fick's first law, which is used in
steady-state diffusion, i.e., when the concentration within the diffusion
volume does not change with respect to time.



=−

Diffusion flux. Equation 2-7

Where: D is the diffusion coefficient or diffusivity,
is the concentration of oxygen in the solution,
x is the position.

And the electrical current caused by diffusion is

=

Diffusions current. Equation 2-8

Where: n is the number of free transported electrons.
F is the Faraday constant.
A is area of the cross section.
x is the position.
is the diffusions flux.

In addition, using Laplace transformation we get[BARD00]:

√ ∗
( )=
√

Diffusion Current respect to time t. Equation 2-9

For current after a long time and a temperature of 25°C, it can be simplify
to:

=4

Oxygen concentration current. Equation 2-10

Where r is radius of the work electrode.[MUGG02]



REGION IV (DISSOCIATION REGION):

Over potential dissociates water molecules. This is visible by the
hydrogen formation in gas form. Solutions without dissolved oxygen have
almost this region only.

2.10.1.2 Equipment and items

VOLTALAB 80:

Voltammetry - Pot. Cyclic Voltammetry:
To get a curve we use a potential ramp as input parameter and read the
current response of the Clark sensor, in the range of zero to -1.4V. To
avoid current flowing through the reference electrode, we use an
auxiliary electrode.

PIN BOX ASSIGNMENT:

Sensor Auxiliary Working Reference
No. electrode electrode electrode
4 22 20 24

Pins assignment of the Clark sensor. Table 2-9

Sensor number 4 on cMOS chips has the same contact pin numbers as the
single sensor on nMOS chips.

SOLUTIONS:

- PBS: Phosphate buffered solution with pH value of 6.5 with from air
dissolves oxygen. The oxygen saturation in PBS has a concentration of
7.8811mg/l or 0.25mM.
- Calibration solution: Na2SO3 (M=126g/mol) added as 1g to 100ml PBS,
enough to bind the oxygen molecules in the PBS solution.



2 + → 2

Chemical reaction to bind dissolved oxygen. Equation 2-11

SERSOR CHIPS

1 2
Reference
elektrode
3 4 5 Working
electrode
Auxiliary
electrode

1mm 250µm

Clark sensor on the cMOS chip. Picture 2-19

Auxiliary
electrode

Working
electrode

reference
1mm 250µm electrode

Clark sensor on the nMOS chip. Picture 2-20

Working electrode is circle shaped and has diameter of 35µm on both chips. The
auxiliary and reference electrodes are surrounding the working electrode in ring
form. The reference electrode is as big as about one third surface area of the
auxiliary electrode. On the cMOS chips, this ring is directly surrounding the
electrode. On the other side, the ring of the nMOS chip has a distance of about
250µm from the working electrode.



The nMOS chip has only one Clark sensor, where the cMOS has 5 Clark sensors.
The single sensor of the nMOS has the same contacts of the sensor number 4 on
the cMOS chips.

2.10.1.3 Measurement assembly

Schematic design of the measuring system. Picture 2-21

Measurement assembly. Picture 2-22



2.10.1.4 Measurement settings and parameters

are to be chosen, in this case 10 / .
- To reduce capacitive effects caused by polarization slower scan rates

An example for a voltammogram voltage. Graph 2-6

−1.4 , so no need to scan more than this value.
- By PBS the disassociation of the water within it begins already below

is in around −10 . Therefore, the range of the measured current
must be within ±1µ , otherwise the Voltalab unit -due the change to a
-

smaller accuracy range- will not be able anymore to detect small
currents in nA range

- The influence of the temperature is to ignore, due the small effect of
the temperature on the diffusions constant, which is under
2%.[HITC78].

=
- The diffusions constant D is an exponential function of temperature T:

Diffusions current. Equation 2-12

Where: is the diffusions constant at a reference temperature,
is the activation energy for diffusion,
R is gas law constant.



2.10.1.5 Procedure

1. Making several cycles at higher scan rate using the setting explained in
the previous chapter will deliver more accurate results.

2. Repeating the measurement again with the same parameters but this time
using a PBS solution without oxygen dissolved in it.

3. Choose an operation point from the tableau region with significant
difference between the measurement with and without oxygen.



2.10.2 IDES Sensor (Impedimetric)

2.10.2.1 Idea

An electrochemical half cell consists of the resistance of the electrolyte solution,
the capacity of the electrochemical double layer q.v. Clark sensor (Amperometry)
and the resistance of the charge transfer. Using impedance measurement we can
calculate the imaginary component as like capacity and the real component as
the resistance.

In order to determine impedance, complex Ohm’s law is used:

( )
=
̅
( )

Complex Ohm’s law. Equation 2-13

For impedance measurement, a two-wire electrical measurement assembly is
used. However, when the impedance to be measured is relatively low, or the
impedance of the probe is relatively high, a 4-point probe measurement will
yield more accurate result.

TWO-WIRE MEASUREMENT METHOD:

A known alternating voltage at a defined frequency is applied across the
unknown impedance Z. This voltage source is alternating symmetric at
zero volts and it should not generate a current. In other words, the
voltage source must have a high resistance at chosen frequency. The
current that flows through the probe is measured. The impedance can
then easily determined by dividing the applied current by the measured
current.

An ideal circuit for measuring an impedance Z. Picture 2-23



The measurements done with two-wire setup include not only the
impedance of the electrolyte but also the impedance of the leads and
contacts. This may be a problem falsifying the results.

When using an impedance meter to measure values above few ohms or
picofarads, this added small impedance is usually not a problem.
However, when measuring low impedances or when contact and lead
resistance and capacity may be high, obtaining accurate results with a
two-wire measurement may be problematical.

Realistic circuit incl. interfering components. Picture 2-24

FOUR-WIRE MEASUREMENT METHOD:

A solution for the problem of two-wire measurements is using the four-
wire measurement setup. Because a second set of probes are for sensing
and since the current I0 though the electrolyte is negligible small, only the
voltage drop across the device under test is measured. As a result,
impedance measurement is more accurate.

Four-wire impedance measurement circuit. Picture 2-25




VOLTALAB 80:

Pot. Fixed Freq. EIS (Capacitance):
To measure the impedance, an alternating sinus voltage is applied and
the resulted current is measured.

PIN BOX ASSIGNMENT:

Sensor Anode Anode No. 2 Cathode Cathode No. 2
IDES 28 29 31 32

Pins assignment of the IDES sensor. Table 2-10
SOLUTIONS:

- De-ionized water.
- PBS: Phosphate buffered saline solution. It has a molar concentration
of about 150mM of NaCl.
- PBS solutions with 75, 225, and 300mM of NaCl.
-

SERSOR CHIPS

- nMOS chips have a visible sensor area of about A=8mm², while cMOS
chips have about one third of it.

2mm

IDES sensor on the nMOS chip. Picture 2-26



1mm

IDES sensor on the cMOS chip. Picture 2-27

The nMOS chip has a polygon shaped IDES and it covers almost the half visual
area of the fluid contact surface. The IDES on the cMOS is much smaller and
rectangular. On the both of the chips, the IDES sensor is placed centered and the
other sensors types is surrounding it.



The impedance measurement assembly is good enough to achieve clear results
using the two-wire method. The Voltalab and the isolated BNC cables have
insignificant effect on the measured values, due its low electrical resistance and
capacity.




To measure the impedance, a voltage of 30mV with a frequency of 10kHz is
applied and the resulted current for 20 seconds is measured.

AC signal for impedance acquisition. Graph 2-7

The applied sinus voltage is alternating at zero with an enough frequency to
avoid current flow.

Influence of frequency on impedance[BRIS06]. Graph 2-8



Using Ohm’s law the impedance can be easily calculated and plotted in real and
complex components.

̅= ̅ + ̅ = +
= ̅ ( )
= ̅ ( )
=2

Real and complex component of impedance. Equation 2-14

2.10.2.5 Procedure

1. Making several cycles using the setting explained in the previous chapter
with a PBS solution of 75mM NaCl.

2. Repeating the measurement again with the same parameters but this time
using PBS solutions with steps of 75mM to 300mM.

3. The resulted measurements should be vary in real component.



2.11 Semiconductor sensors

Semiconductor sensors are in contrast to the non-semiconductor sensors have
structures within the silicon semiconductor layer. Temperature diode, ISFET and
CV/O2-FET all share the silicon layer with different doped regions.

2.11.1 Temperature Diode (Potentiometry)

Temperature change effects the properties of semiconductors, and this will
falsify the measurements. Therefore sensors falsified by temperature must be
adjusted with a correction factor relatively to the temperature. When using living
cells the cell activity is temperature dependent.

2.11.1.1 Idea

The characteristic curve of a p-n diode shows a direct temperature dependency.
This can be explained with the electronic band structure model. Operating such a
diode with a current in forward bias and a voltage , gives us Schockley’s
diode law [MSZE98]:

= ( − 1)

Schockley’s diode law. Equation 2-15

For ≫ =

Schockley’s simplified diode law. Equation 2-16

Where: is the thermal diode current,
is the saturation current,
is the voltage across the diode,
is the thermal voltage.

The diode equation in respect of voltage can be written as:



=

Diode law in respect to voltage. Equation 2-17

The thermal voltage UT is a known constant defined by:

=

Thermal voltage. Equation 2-18

Where: q is the magnitude of charge on an electron (elementary charge),
k is Boltzmann’s constant,
T is the absolute temperature of the p-n junction in kelvins.

The voltage change is −2.25 / in the range from −50° to +150°C. [STEP06].
So is approximately 26 mV at room temperature of 300K. [MOHR00].

I-V characteristic curve of a diode and the influence of temperature. Graph 2-9




INCUBATOR:

For a constant and adjustable environment temperature.

VOLTALAB 80:


To get a diode curve we use a potential ramp as input parameter and
read the current response of the diode, in the range of zero to 3V.

Pulse - Chrono Potentiometry:

At chosen fixed work current we measure the voltage as a function of the
temperature change.

PIN BOX ASSIGNMENT:

Sensor cathode Anode
TD 5 6

Pins assignment of the temperature diode. Table 2-11

SERSOR CHIPS

1mm 15µm

Temperature diode on the cMOS chip. Picture 2-29



1mm 30µm

Temperature diode on the nMOS chip. Picture 2-30

The diode on the nMOS chip has a remarkable bigger area than the pn diode of
the cMOS. This will cause different behavior for the temperature dependency.
The pn diode is isolated with the protection layer and therefore it has no direct
contact to the electrolyte. This makes the temperature sensor electrolyte
independent, so there is no aging caused by contacting with fluids.



For fast tests, fluids with different temperatures can be used instead of the
incubator. But characterizing and long term measurements are not possible due



the small amount of the fluid (7µl), which has a smaller heat capacity than the
sensor chip. So, the fluid will get the temperature of the chip in a short time.


A diode characteristic curve is U-I curve. That means we measure the current in
dependence on the applied voltage. Instead of choosing voltage as an operation
point and measuring its current, we set a current as operation point and measure
it’s correspond voltage. That is because the voltage is easier and more accurate
to measure using a simple electrical circuit than measuring a current.

The supplied current can be easily generated with a voltage to current amplifier
circuit.

2.11.1.5 Procedure

1. Make a fast test to determine the resulted current range within a voltage
from zero to 3 volts. Our target is to get smallest current as an operation
point. A higher current causes more internal heating of the diode, which is
not only falsifying the real temperature of the sample, but it can also rise
its temperature to unwanted values especially for living cells.

2. At room temperature, measuring the current for a given voltage ranging
from zero to maximal 3 volts, and repeat it at higher temperatures. It’s not
to forget, that in the course of the day, the room temperature can be vary
according to the sunlight, operating of electrical equipment and the
number of persons sharing the same room. All this produce extra heat in
the room and may cause to bias the results. So using an incubator with a
temperature a little above room temperature will give a more clear result
without having temperature variations when measuring. 27°C seems to be
easy to realize and keep constant by the incubator.

The used incubator needs about an hour to heat up and to remain at a
constant temperature, and another one after reaching the target
temperature, to let the sensor chips and its terminal box also to reach this
temperature.

3. Determining the best operation point, at lowest current with significant
temperature influence. This can be done easy by reversing the voltage-
current U-I curve to current-voltage I-U curve and selecting the biggest
voltage range at the same current.



2.11.2 Reference MISFET (nMOS)

2.11.2.1 Idea

MISFET [HENN05]. Picture 2-32

A MISFET is an active part. It works like a voltage controlled resistor. It has three
ports (electrodes): Gate, Source and Drain.

As basic material a low p doped silicon substrate is used. In this substrate two
high n doped regions are embedded. These two regions make the drain and
source ports. Between these two regions there must be a p doped region so we
get an npn structure. Though this npn flows for now no current, because it is like
a np diode which is connected afterwards with a pn diode. When the first diode
allows flowing current through it, the second one will block it.

Above the p doped region, which is between the n regions, is an isolation layer
and then a metal layer. This construction builds the gate port.



By applying a potential at the gate port, an electrical field is created, which
creates within the embedded p region an n electrons channel. The size of this
channel is proportional to the gate potential.

Source-drain current. Graph 2-10, Picture 2-33

Usually source and drain pins are interchangeable, but the manufacturing may
be not made symmetric.

The MISFET has three operation modes:

CUT-OFF, SUB-THRESHOLD OR WEAK INVERSION M ODE:

This operation mode is when the gate-source voltage UGS smaller than
threshold voltage of the device Uth.

The transistor is turned off. This means there is ideally no current flows
through the transistor, because there is no conducting n-channel between
source and drain. In reality, the Boltzmann distribution of electron
energies is allowing some electrons at the source to enter the n channel
and flow to the drain. This results in a sub-threshold leakage current.



LINEAR/OHMIC REGION OR TRIODE MODE:

This operation mode is when the gate-source voltage UGS bigger than the
threshold voltage Uth and drain-source voltage is smaller than the
difference between source-gate UGS and threshold Uth voltages.

The transistor is turned on. This means, that the n channel between the
drain and source has been created: This allows current to flow through
the transistor. The MISFET operates in this mode like a controllable
resistor. This can be done by the gate voltage. This current has also
dependency on the gate’s width and length and the isolating layer
electrical capacity

SATURATION MODE OR ACTIVE MODE:

This operation mode is when the gate-source voltage UGS is bigger than
the threshold voltage Uth and drain-source voltage is bigger than the
difference between source-gate UGS and threshold Uth voltages. The
transistor is turned on. This means that the n channel between the drain
and source has the maximal capacity, which allows current to flow
through it. The drain current is now weakly dependent upon drain
voltage and controlled primarily by the gate-source voltage.


VOLTALAB 80:

To get the characteristic curve of the ISFET we use a potential ramp as
input parameter and read the current response.

VOLTAGE SOURCE:

Applying several voltages on the gate port, to control the current
between source and drain.

PIN BOX ASSIGNMENT:

Drain Gate Source
REF-
63 64 65
MISFET




SERSOR CHIPS

Chip No. of sensors Gate area
nMOS 1 3x100µm²
cMOS 0 n/a


The reference transistor is identical in contraction to the ISFET sensor, which is
described and evaluated in the next chapter. The characteristic curves of the
reference are in the same range of the ISFET. So a malfunction of the reference is
a good indicator for the malfunction ISFET, without using any fluids to test.

1mm 100 µm

Reference MISFET on the nMOS chip. Picture 2-34

Above is a picture of the die. The MISFET is located in the top right corner of it.
The transistor can be seen only before the packaging. The package for the
protection of the bonding and the plastic fluid reservoir above it covers the
transistor completely.





No need for fluids to operate the reference transistor. Transistors have
temperature dependency, so operating the transistor for a long time may cause
to heat and that will effect the measuremesnt. Using fluid can make the transistor
heating being less, and that’s by taking some heat from the surface of the chip to
the fluid.


For the characteristic curve of the reference MISFET, the used potential
ramp of the UDS is in the range of 0V to 5V. The UGS is in 1V steps from 0V
to 5V.

2.11.2.5 Procedure

1. Measuring IDS while applying UDS in a ramp from 0 to 5V. The power
supply is not yet connected the gate port.

2. Repeating the measurement of IDS while increasing USG in 1V steps from
0V to 5V.



2.11.3 ISFET Sensors for pH-Measurement

2.11.3.1 Idea

The pH of a solution is dependent on the concentration of hydrogen ions or
its correspondent hydroxide ions. The higher is the concentration of
hydroxide ions in a solution, the higher is its pH value.

= −log [ ] = 14 − = 14 + log [ ]
∆ ( ) = − log [ ( )] = 14 + log [ ( )]

pH value dependency on the concentration of . Equation 2-19

ISFET has an ion sensitive layer. On this layer the gathering ions create a
potential. This potential is the ISFET controlling potential of gate. The n-channel
within the semiconductor of the ISFET is established and allows the current to
flow though the transistor from source to drain. The higher is the gate vs. source
potential, the wider is the n-channel and higher is the current flow from source
to drain.

Effect of the hydroxide on the source drain current. Graph 2-11, Picture 2-36




VOLTALAB 80:

To get the characteristic curve of the ISFET we use a potential ramp as
input parameter and read the current response.

Pulse - Chrono Potentiometry:
At chosen fixed work current we measure the voltage as a function of the
pH change.

PIN BOX ASSIGNMENT:

Drain Source
ISFET A 1 2
ISFET B 3 4
ISFET C 7 8
ISFET D 9 10
ISFET E 18 15

Pins assignment of the ISFET sensors. Table 2-14

ISFET E is also in the same time an O2-FET with a surrounding NME.

SOLUTIONS:

- PBS: Phosphate buffered saline solution with a pH value of 7.3
- A seconds PBS solution with a pH of 6.8.

REFERENCE ELECTRODE:

- Ag-AgCl electrode.



SENSOR CHIPS

Gate
Drain Source

1mm 100µm

ISFET sensor 4 on the cMOS chip. Picture 2-37

Gate
Drain Source

1mm 100µm

ISFET sensor on the nMOS chip. Picture 2-38

The placing of the ISFET sensors on both chips is different. While the sensors on
cMOS chip are evenly distributed on the chip surface, the ones of the nMOS chip
are on the both sides of the IDES sensor, which is located in the middle of the
chip.




Measurement assembly of the project. Picture 2-39

The power supply seen in the picture above is used experimentally to raise the
gate voltage by raising the reference potential. q.v. “Loosing of the passivation
layer” in chapter 4.2 on page 100.



Endversion1 skriptum characterization of miscellaneous multi parametrical silicon based biosensor chips

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