Low-cost organic gas sensors on plastic for distributed environmental sensing

Vivek Subramanian

Department of Electrical Engineering and Computer Sciences

University of California, Berkeley

RD83089901

Arrayed Gas Sensors

Substrate

Molecule inambient

A B C D

GenerateChemical

Signatures

Map Responses

Pixel Array Index

Sen

sor

Par

am

ete

r

Responses to differentmolecules

Distributed environmental monitoring

• Need for distributed monitoring- Identification of environmental hazards- Triggering of proactive action- Development of accurate environmental models

• Sensor Requirements- Ultra-low-cost- Ease of dispersal- Trainability / adaptability

• Our Approach: Arrayed organic FETs- Easily arrayed at low-cost via printing- Flexible for easy dispersal- Trainable via electronic nose architecture

Printing: a pathway to low-cost

Print System Print System

No lithographyNo vacuum processing (CVD, PVD, Etch)

Reduced abatement costsCheap substrate handlingReduced packaging costs

Printed Transistors

Substrate

Gate electrode is printed usinggold nanocrystals

Substrate

Low-temperature anneal forms gate stripeto edge of array (out of page)

Substrate

Polymer dielectric is depositedvia inkjet

Low-temperature anneal forms S/D stripesand connections (in plane of page)

Various active layers are deposited via inkjet

Substrate

Source / Drain contacts areprinted using gold nanocrystals

Substrate

Substrate

Plans & Current Status• Year 1:

- Development of baseline arrayed sensor process- Sensor Characterization- Development of arrayable materials

• Year 2:- Array demonstration- Development of signature table for above arrayed sensor- Characterization of 2nd generation targets

• Year 3:- Optimization of arrayed sensors- Characterization of real-time monitoring - Characterization of fluid sensing using organic gas sensors- Optimization of derivatives for sensing applications.

Baseline sensor screening process

S D

G

Materials are characterized using a

substrate-gated architecture (easy

fabrication for rapid screening)

A silicon substrate enables easy I/O via an edge connector

The channel is exposed to the analyte, resulting in performance changes

Sensor Characterization

Agilent 4156

To ensure accuracy, measurements are performed with a calibrated

precision semiconductor parameter analyzer.

Switching between individual sensors is performed via a

switch matrix PCB

Experimental Setup

N2

Mass FlowController

AnalyteDelivery

Valve

Valve

SensorChamber

Bubbler

Exhaust

Exhaust

Agilent 4156

MassFlowMeter

Valve

Sensor RepeatabilityId-Vd (Zoomed)

-3.00E-08

-2.50E-08

-2.00E-08

-1.50E-08

-1.00E-08

-5.00E-09

-2.60E+01 -2.10E+01 -1.60E+01 -1.10E+01 -6.00E+00

Vd (Volts)

Id (

Am

ps)

Baseline Toluene Regen

Multiple cycles can be performed with full regeneration

Multi-parameter sensingTransconductance

baseline 60 sccm regen 100 sccm regen

0.00E+00

2.00E-09

4.00E-09

6.00E-09

8.00E-09

1.00E-08

gm

(S

)Threshold Voltage

baseline 60 sccm regen 100 sccm regen

-1.00E+01

-8.00E+00

-6.00E+00

-4.00E+00

-2.00E+00

0.00E+00

V (

Volt

s)

Mobility

baseline 60 sccm regen 100 sccm regen

0.00E+005.00E-051.00E-041.50E-042.00E-042.50E-043.00E-043.50E-044.00E-044.50E-04

u (

cm

2/V

s)

Drain Current

baseline 60 sccm regen 100 sccm regen

-1.60E-07

-1.40E-07

-1.20E-07

-1.00E-07

-8.00E-08

-6.00E-08

-4.00E-08

-2.00E-08

0.00E+00

Id (

Am

ps)

Sensor dynamics – transient responseChange in Drain Current Under Toluene Exposure

-5.00E-09

-4.50E-09

-4.00E-09

-3.50E-09

-3.00E-09

-2.50E-09

-2.00E-09

-1.50E-09

-1.00E-09

-5.00E-10

0 30 60 90 120 150

Time (Minutes)

Id (

Am

ps

)

Sensor response can be very slow, due to slow analyte absorption. Speed can be increased by reducing film thickness

Differential sensitivity – pathway to an electronic nose?

Nose Response to Water (Pentacene)

-2.20E-06

-2.00E-06

-1.80E-06

-1.60E-06

-1.40E-06

-1.20E-06

-1.00E-06

0 10 20 30 40

Time (Minutes)

Id (

Am

ps)

Nose Response to Water (P3HT)

-1.50E-07

-1.40E-07

-1.30E-07-1.20E-07

-1.10E-07

-1.00E-07

-9.00E-08-8.00E-08

-7.00E-08

0 10 20 30 40

Time (Minutes)

Id (

Am

ps)

Nose Response to Water (P3OT)

-4.50E-08

-4.00E-08

-3.50E-08

-3.00E-08

-2.50E-08

-2.00E-08

-1.50E-08

0 10 20 30 40

Time (Minutes)

Id (

Am

ps)

Demonstration of basic electronic nose functionality

Nose Response to Water and Milk

30

40

50

60

70

80

90

100

110

0 10 20 30 40

Time (Minutes)

Pe

rce

nta

ge

of

Ba

se

line

Cu

rre

nt

Pentacene P3OT P3HT

WaterMilk

Organic Transistor Stability

0

0.002

0.004

0.006

0.008

0.01

7/14 7/15 7/16 7/17

Time (Date)

Mo

bili

ty (

cm

2 /Vs

)

-4.E-07

-3.E-07

-2.E-07

-1.E-07

0.E+00

Dri

ve

Cu

rre

nt

(A)mu (sat)

mu (lin)

Ion (sat)

Implication: We must either improve dielectric interface or use VT-insensitive differential sensing method

Interaction Mechanisms

Ion Change in P3HT due to Ethanol

0

20

40

60

80

100

120

-1 1 3 5 7 9Time (min)

Perce

nt of B

aseline Value

12 nm

75 nm

100nm

Ion Change in P3HT due to Acetic Acid

0

20

40

60

80

100

120

-1 4 9 14 19 24Time (min)

Perce

nt of B

aseline va

lue

12 nm 40 nm 75nm

100 nm 12 nm 40 nm

75nm 100 nm

Baseline Baseline

- Sensors show a wide range of interactions, complicating analysis. Interactions include:

• Polar group interactions• Chain / bulk interactions• Swelling

Conclusions & Future Work• Organic FET-based sensors show promising

responses, including transient behavior and cycle life

• Work remains to optimize structure and process flow, particularly in terms of stability and reliability

• Future Work:

- Integration of latest sensing materials into printed device architecture

- Deployment in testing of environmentally-relevant analytes- Enhancement of specificity through functionalization / doping