The focus of this work would be to exploit the vapor detection technology developed recently at Caltech that forms the basis for a low power, simple "electronic nose". In this work we have integrated the sensors, signal preprocessing, signal processing, and data analysis functions into a single, low power, low cost, "nose chip". Such a device could be implantable covertly or overtly onto suspect sites, deployable through remote delivery methods, worn by soldiers for CW alerts and in principle for IFF or military/nonmilitary identification purposes, and for other areas of national security where low power, lightweight, small, chemical sensing is of importance

Lewis, Nathan S.

English

Caltech Authors - Main

A VLSI Compatible Conducting Polymer Composite Based "Electronic Nose" Chip 
Nathan S. Lewis 
Professor of Chemistry 
Division of Chemistry and Chemical Engineering, 127-72 
Noyes Laboratory 
Pasadena, CA 91125 
ABSTRACT 
The focus of this work would be to exploit the vapor 
detection technology developed recently at Caitech that 
fonus the basis for a low power, simple "electronic nose", 
In this work we have integrated the sensors, signal 
preprocessing, signal processing, and data analysis 
functions into a single, low power, low cost, nnos~ chip". 
Such a device could be implantable covertly or overtly onto 
suspect sites, deployable through remote delivery methods, 
worn by soldiers for CW alerts and in principle for IFF or 
military/nonmilitary identification purposes, and for other 
areas of national security where low power, lightweight, 
small, chemical sensing is of importance. 
INTRODUCTION 
The basis for Qur approach involves an effort at Caltech 
that has recently led to arrays of simple, readily fabricated, 
chemically sensitive conducting polymer films (1-3). An 
array of sensors that individually respond to vapors can 
produce a distinguishable response pattern for each separate 
type of analyte or mixture. Pattern recognition algorithms 
and/or neural network hardware are used on the output 
signals arising from the electronic nose to classify, identify, 
and where necessary quantify, the vapor or odors of 
concern (4-5). This response is much like the way the 
mammalian olfactory sense produces diagnostic patterns 
and then transmits them to the brain for processing and 
analysis. 
The underlying principle of the Caltech electronic nose 
is extraordinarily simple. When a polymer film is exposed 
to a gaseous vapor, some of the vapor partitions into the 
film and causes the film to swell (Fig la). This swelling is 
probed electrically because the sensor films each consist of 
a composite that contains regions of a conductor that have 
been dispersed into the swellable organic insulator. The 
vapor-induced film swelling produces an increase in the 
electrical resistance of the film because the swelling 
decreases the number of connected pathways of the 
conducting component of the composite material. Any 
individual sensor film responds to a variety of vapors, 
because numerous chemicals will partition into the polymer 
and cause it to swell to varying degrees (Fig Ib) (6). 
However, an array of sensors, containing different 
polymers, yields a distinct fingerprint for each odor because 
the swelling properties over the entire array are different for 
different vapors. 
The pattern of resistance changes on the array is 
diagnostic of the vapor, while the amplitude of the patterns 
indicates the concentration of the vapor. An example of the 
different patterns produced by various different vapors on 
the electronic nose is provided in Fig. 2. The 
swellingldeswelling process is highly reversible in thin 
polymer films, so that typically thousands of cycles can be 
performed without significant loss of responsivity of the 
detectors. The detectors have been shown to respond to 
analyte concentrations in the low ppb range under certain 
conditions, with more specific chemistries allowing 
detection in targeted cases, such as biogenic amines for 
health/disease differentiation, in the ppt range. 
insulating polymer matrix 
conducting element 
e 
A 
- • 
Ca) 
80% poly(butadiene)/20% CB composite 
linear rMpt>nSe to diver~ ... ~nlv"'Qts 
'~r----------------------' 
1000 
'""t ~~~ "~ .\.--J 
000 050 100 150 200 250 300 
(b) 
B 
__ wop.",,1 
_b€n,,,,,e 
;-chlorolO!m 
~cyclol1e'.none 
1"-hept.no 
Fig. la Swelling occurs as an odorant partitions into the polymer. (b) A 
linear response of an individual sensor signal as a function of 
concentration is observed for a variety of analytes. 
19,1.1 
0-7803-7462-2/02/$17.00 ©2002 IEEE IEDM 485 
[I Methanol. Ethyl Acetate:: Benzene 
o. 
o. 
o. 
o. 
Sensor Number (normalization factor) 
(a) 
PC' 
(b) 
Fig. 2a. Response patterns for three different solvents on a 17 element 
sensor array. (b) Data in principal component space from a 20-detector 
array exposed to n-tetradecane, n-dodecane, n-decane, n-nonane, n-octane, 
and n-heptane each at P/po = 0.005 to 0.03 in air (with po being the vapor 
pressure of the analyte at 300 K), showing th.at the pattern type identifies 
the vapor and the magnitude of the pattern signals is linearly proportional 
to the analyte concentration. 
We have fabricated "nose-chips", which consist of 
arrays of pixels in which each pixel contains a different 
composition of polymeric sensor and the signals are fed to a 
common pinout using a simple row/column multiplexing 
addressing scheme. This chip is a component of an 
integrated system, all on one chip, that contains the entire 
functionality spanning sample introduction, data 
acquisition, signal preprocessing, adaptation, filtering, and 
signal processing functions. Development of the necessary 
compatible technologies, along with their integration, and 
determination of the performance of the resulting "nose 
chip" system for targeted applications of interest to national 
security applications, is the focus of some of the future 
work to be discussed in this presentation. 
R&D GOALS/APPROACH 
We have fabricated some preliminary "nose-chips", 
which consist of arrays of pixels in which each pixel 
contains a different composition of polymeric sensor and 
the signals are fed to a common pinout using a simple 
row/column multiplexing addressing scheme (Fig. 3). This 
chip demonstrates the validity of the approach but is not an 
integrated system, all on one chip, that contains the entire 
functionality spanning sample introduction, data 
acquisition, signal preprocessing, adaptation,. filtering, and 
signal processing functions. Development of the necessary 
compatible technologies, along with their integration, and 
determination of the performance of the resulting "nose 
chip" system for targeted applications of interest to national 
security applications, will be discussed. 
Fig. 3. Photograph of a "nose-chip", with 12 coluITUls and 6 rows, each 
having a different polymeric sensor combination and each pixel having a 
switch under its pair of contact lines. A single pinout provides the output 
of the sensor pixel being interrogated using a row/column addressing 
scheme. 
Figure 4 shows the schematic of the unit serisor cell. The 
cell consists of a switch transistor and decoding logic. The 
availability of only two metals layers in the Ie process 
required transistors at each sensor cell to perform decoding. 
This circuitry (MI-M4) decodes X and Y selection signals 
generated by shift registers on the periphery of the array. 
This selection signal controls a switch (M7) that toggles a 
current (I;,) through the resistive sensor. In this design only 
one sensor is energized at a time to reduce power 
consumption. To reduce noise and the switch resistance, 
transistor M7 occupies most of the sensor area. The 
decoding circuitry also selects a transmission gate 
19.1.2 
486-IEDM 
(M5,M6,M8,M9) which passes the sensor voltage to a 
column output bus. This signal is amplified and transmitted 
off-chip for processing. The decoding circuitry is 
complicated because the sensor occupies one of two 
available metal layers in the fabrication process we used for 
this chip, precluding the use of a simplified bus scheme. 
lin 
VM 
ROW 
Figure 4. Schematic of three wire sensing celL Transistors MI-M4 form a 
NAND gate to select the cell, M7 switches the current source on sensor 
resistor, and M5,M6,M8,M9 form a transmission gale to select the output 
on a column output line. The column output is buffered and passed off-
chip. 
A 0.5 cm X 0.25 cm chip, with 492 sensors arranged as an 
array of 41 X 12 sites, was fabricated in a 2.0 micron 
process through the MOSIS design service. There are two 
contacts to the sensor: one with the drive switch M7. and 
another connecting the sensor to signal ground. The 
ground terminal is laid out as a ring around the perimeter of 
the cell and is common to all sensors. The interior of each 
cell contains the drive contact for the sensor. The ring 
structure was motivated by difficulties encountered in early 
sensor deposition trials -the carbon black particles would 
aggregate along the perimeter of a deposited sensor, 
creating a low resistance path. Moreover, the ring structure 
allows us to experiment with depositing mixtures of sensor 
materials across the chip[5]. We deposit the sensor 
polymer between these two contacts, directly on top of the 
active circuitry. We make the sensors rectangular to 
increase the contact area for the interior contact, as well as 
to reduce contact noise and lIf noise due to the non-uniform 
electrical field[6]. 
We use a standard commercial foundry for the 
fabrication of the integrated circuits. The top layer of 
Aluminum is used for the sensor contact. Unfortunately, 
the native aluminum oxide that forms on the contacts 
prevents depositing the sensors without a post-processing 
step. Since dedicated wafer runs are cost prohibitive for 
small prototyping runs, this step must be performed on the 
individual chip die returned from the foundry. This 
precludes the use of a conventional mask based approach, 
since it is difficult to use a resist mask on an individual die. 
To create suitable contacts we use an electroless NiJAu 
process that requires no masking from Stapleton 
Technologies (Long Beach, California). This process can 
be performed easily on individual die with simple 
equipment and requires only seven procedures: four 
involving cleaning and surface preparation and three plating 
steps. The surface preparation involves an acid zincate 
process to remove the native oxide and activate the 
aluminum surface. This is followed by the three plating 
steps. Nickel is plated first, followed by a two stages of 
gold plating: a monolayer process that plates the Nickel and 
then a build up stage that finishes the plating. In addition 
to creating a nonreactive surface for the sensor contacts, the 
plating also creates wells that help constrain the sensor 
material during deposition. 
CONCLUSION 
We have demonstrated the successful integration of a 
chemical sensor array with a standard CMOS process. 
Following a simple post processing operation we are able to 
deposi t sensor material on the surface on an integrated 
circuit. By depositing different sensor materials we are 
able to create an array capable of discriminating analytes. 
We plan to create larger arrays with a large number of 
different polymers, and arrays with additional active 
circuitry such as amplification and adaptation. Our ultimate 
goal is a chip with several thousand integrated sensors, 
combined with active processing circuitry. Intimate 
integration of active circuitry and sensor not only enables 
large arrays, but also is essential in overcoming the 
historical limitations of polymer-based sensors. We believe 
that our approach can create small, inexpensive, low power 
and even wearable chemical sensor arrays that rival the 
detection and discrimination capabilities of mammalian 
olfaction. 
REFERENCES 
(I) M.e. Lonergan, E.J. Severin, BJ. Doleman, S.A. Beaber, RH. 
Grubbs, and N.S Lewis, "Array-Based Vapor Sensing Using 
Chemically Sensitive, Carbon Black-Polymer Resistors," Chern. 
Mater., vol. 8, pp. 2298-2312,1996. 
(2) EJ. Severin, BJ. Doleman, and N.S. Lewis, "An Investigation of 
the Concentration Dependence and Response to Analyte Mixtures 
of Carbon Black/Insulating Organic Polymer Composite Vapor 
Detectors," Anal. Chern., vol. 72, pp. 658-668, 2000. 
(3) BJ. Doleman, R.D. Sanner, EJ. Severin, R.H. Grubbs, and N.S. 
Lewis, "Use Of Compatible Polymer Blends To Fabricate Arrays 
Of Carbon Black-Polymer Composite Vapor Detectors," Anal. 
Chern., vol. 70, pp. 2560-2564, 1998. 
(4) BJ. Doleman, M.e. Lonergan, E.J. Severin, T.P. Vaid, and N.S. 
Lewis, "Quantitative Study of the Resolving Power of Arrays of 
Carbon Black-Polymer Composites in Various Vapor-Sensing 
Tasks," Anal. Chern., vol. 70, pp. 4177-4190,1998. 
(5) T.P. Vaid, M.e. Burl, and N.S. Lewis, "Comparison of the 
Performance of Different Discriminant Algorithms in Analyte 
Discrimination Tasks Using an Array of Carbon Black-Polymer 
Composite Vapor Detectors," Anal. Chern., vol 73, pp. 321-331, 
2001. 
(6) EJ. Severin and N.S. Lewis, "Relationships among Resonant 
Frequency Changes on a Coated Quartz Crystal Microbalance, 
Thickness Changes, and Resistance Responses of Polymer-Carbon 
Black Composite Chemiresistors," Anal. Chern., vol. 72, pp. 2008-
2015,2000. 
19.1,3 
IEDM 487 


A VLSI compatible conducting polymer composite based "electronic nose" chip

An Investigation of the Concentration Dependence and Response to Analyte Mixtures of Carbon Black/Insulating Organic Polymer Composite Vapor Detectors,&quot;

Array-Based Vapor Sensing Using Chemically Sensitive, Carbon Black-Polymer Resistors,&quot;

Comparison of the Performance of Different Discriminant Algorithms in Analyte Discrimination Tasks Using an Array of Carbon Black-Polymer Composite Vapor Detectors,&quot;

Quantitative Study of the Resolving Power of Arrays of Carbon Black-Polymer Composites in Various Vapor-Sensing Tasks,&quot;

Relationships among Resonant Frequency Changes on a Coated Quartz Crystal Microbalance, Thickness Changes, and Resistance Responses of Polymer-Carbon Black Composite Chemiresistors,&quot;

Use Of Compatible Polymer Blends To Fabricate Arrays Of Carbon Black-Polymer Composite Vapor Detectors,&quot;

http://authors.library.caltech.edu/27525/1/LEWiedm02.pdf

A VLSI compatible conducting polymer composite based "electronic nose" chip

Abstract

Similar works

Full text

Available Versions

Caltech Authors - Main