Cumming [Mode de compatibilit ]) - Genopole Réussir en ...€“ By happy coincidence SiN is widely...

Integrated Sensors

© University of Glasgow, 2009

David Cumming

Department of Electronics and Electrical Engineering

University of Glasgow

Outline

• Microelectronics

• Medical Devices

• Sensing-system-on-chip


• Sensing-system-on-chip

• Extracellular ion imaging

Cheap mass manufactured technology


Moore’s Law

• Dimensions get smaller

• Number of transistors per chip increases

• Operating voltage


• Operating voltage decreases

• Power consumption decreases

• Memory size increases

Established – Cheap - Available

More than Moore

• Moore’s Law – indicates likely progress of

microelectronics in traditional sectors

• In More than Moore we push microelectronic

technologies into new sectors, and combine with

known strengths


known strengths

– Sensors, biomedical devices, assay and instrumentation on a chip

OR

– SENSING-SYSTEM-ON-CHIP

Laboratory-in-a-Pill


(LIAP)

Endoscopy


Stomach ulcer Polyposis Ulcerative colitis

The Diagnostic Pill

• Use once, throw away


Earliest work

• Components

– 1 pressure sensor

– 1 transistor

– 1 battery


– 1 battery

– 10 ft string

• Enabling technology

– the transistor

R. S. Mackay Berkeley, 1959

Can do much more now

• Pressure – gut motility

• Video - imaging

• Temperature - hyperthermia


• Temperature - hyperthermia

• Dissolved oxygen - post trauma

• pH – acid reflux

• Tumour markers - cancers

• Glucose/fatty acids – foods and digestion

Laboratory-on-a-Chip

• Miniaturisation of analytical systems

• Microfluidics

• High speed

DO NOT SCALE


• High speed

• Multi-process

• Multi-sensor– Temp

– pH

– DO

– Conductivity (σ)

2 mm

Small ASIC

• Single chip comprising

• Microcontroller

• ROM and RAM

• 8 Instrument channels


• 8 Instrument channels

• pH, T, DO, σσσσ

• Data conversion

• Wireless encoder

5 mm

0.6 µm 2 poly 2 metal

CMOS from AMS via

Europractice

Package it up

• Separate components on small PCB

• Connections (interconnect) take up lots of space for little functional reward

• Batteries are large (!)

Sensors


• What can be done with a single chip?

– Using CMOS that is widespread

– Reduce size

– Reduce power

• Sensing-System-on-Chip

ASIC/SoCBatteries

Sensing-System-on-Chip


Single chip digital pH meter

Ion Sensitive Field Effect Transistor

H+

H+

H+

H+

H+

H+

H+

H+

RE

G


� ISFET threshold voltage proportional to pH

silicon dioxide

S

P substrate

DN well

sensing area

silicon

H

H+

H

H+

A CMOS Compatible ISFET

H+

H+

H+

H+

H+

H+

RE

G

silicon nitride

H+

sensing area

H+

H+

H+

H+

H+

RE

G


silicon dioxide

S

P substrate

DN well

sensing area

silicon

H+

H+

H+

H+

H+ silicon dioxide

D S

silicon dioxide

silicon nitride

silicon oxynitride

� Floating gate

ISFET Materials/Characteristics

• pH sensitive materials

– Surface charge varies with pH

– Silicon nitride gives a Nernstian response

– By happy coincidence SiN is widely used passivation layer on CMOS


passivation layer on CMOS

• CMOS-compatible

• Sensitivity ~ 47

mV/pH

pH meter chip


4 m

m

SSOC Readout

Cell-Based Assay Chips


Silicon meets life

Proton imaging

• Image sensors commonplace

– Cameras, CMOS or CCD pixel arrays

– Capture photons

• Biological imaging with photons widespread


• Biological imaging with photons widespread

• Can we be more direct?

– Imaging with ions

• Build CMOS imaging arrays for protons

• Functionalise post-fabrication

Starting point


• The ISFET

• It’s a proton sensor (proton = H+ → pH)

• Need array version

Interface Electronics

• Column of pixels– Addressable elements

– S/D follower

• Readout circuitry– Decoding and

multiplexing


Implementation

• Foundry technology.– Standard 0.35 µm CMOS process– Access via Europractice IC service

• Cross-section through ISFET.


Polysilicon

Metal 1Metal 2Metal 3

Via holes

Passivation

W/L = 1/0.35 µm

Packaging

• Encapsulation • Micrograph


• Cloning ring.

Threshold Voltage Modification

• Test circuit • Effect of UV exposure• Pixel layout


• Apply bias to change conduction band level in ISFET bulks

• UV radiation excites electrons to overcome energy barrier of oxide

• Population on floating electrodes achieves equilibrium with those in bulks after 10 hr

Surface Topography

• 16 x 16 array• 2 x 2 array


• Frame border

• Pixel: 11.6 x 11.6 µm2

• Spacing: 0.6 µm

• Step height: 600 nm

• Pixel: 3 x 6 µm2

• Spacing: 10 µm

Glycolysis Bioassay

• Sensor array• Example pixel


• Decrease in pH due to lactate (before addition of glycolysis inhibitor) and CO2 diffusing out of cells into medium

• Increase in pH due to vanishing [H+] in micro-environment between cells and sensor array surface

Summary

• Diverse range of technologies under

investigation

• Leveraging biotech out of well-established

microelectronics technology


microelectronics technology

• The technology is reasonably mature

• Opportunities for biochemists to explore

Cumming [Mode de compatibilit ]) - Genopole Réussir en ...€“ By happy coincidence SiN is widely...

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