Integrated Sensors. David Cumming Department of Electronics and Electrical Engineering University of Glasgow

Transcription

1 Integrated Sensors David Cumming Department of Electronics and Electrical Engineering University of Glasgow

2 Outline Microelectronics Medical Devices Sensing-system-on-chip Extracellular ion imaging

3 Cheap mass manufactured technology

4 Moore s Law Dimensions get smaller Number of transistors per chip increases Operating voltage decreases Power consumption decreases Memory size increases Established Cheap - Available

5 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 Sensors, biomedical devices, assay and instrumentation on a chip OR SENSING-SYSTEM-ON-CHIP

6 Laboratory-in-a-Pill (LIAP)

7 Endoscopy Stomach ulcer Polyposis Ulcerative colitis

8 The Diagnostic Pill Use once, throw away

9 Earliest work Components 1 pressure sensor 1 transistor 1 battery 10 ft string Enabling technology the transistor R. S. Mackay Berkeley, 1959

10 Can do much more now Pressure gut motility Video - imaging Temperature - hyperthermia Dissolved oxygen - post trauma ph acid reflux Tumour markers - cancers Glucose/fatty acids foods and digestion

11 Laboratory-on-a-Chip DO NOT SCALE Miniaturisation of analytical systems Microfluidics High speed Multi-process Multi-sensor Temp ph DO Conductivity (σ) 2 mm

12 Small ASIC Single chip comprising Microcontroller ROM and RAM 8 Instrument channels ph, T, DO, σ Data conversion Wireless encoder 0.6 µm 2 poly 2 metal CMOS from AMS via Europractice 5 mm

13 Package it up Separate components on small PCB Connections (interconnect) take up lots of space for little functional reward Batteries are large (!) What can be done with a single chip? Using CMOS that is widespread Reduce size Reduce power Sensing-System-on-Chip Batteries Sensors ASIC/SoC

14 Sensing-System-on-Chip Single chip digital ph meter

15 Ion Sensitive Field Effect Transistor G RE H + H + H + H + H + H + H + H + H + H + sensing area silicon dioxide S N well P substrate D silicon ISFET threshold voltage proportional to ph

16 A CMOS Compatible ISFET G RE H + H + H + H + H + H + H + H + H + sensing area H + H + H + silicon nitride H + silicon oxynitride H + H + H + sensing area silicon dioxide S D N well S D P substrate silicon Floating gate

17 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 CMOS-compatible Sensitivity ~ 47 mv/ph

18 ph meter chip 4 mm SSOC Readout

19 Cell-Based Assay Chips Silicon meets life

20 Proton imaging Image sensors commonplace Cameras, CMOS or CCD pixel arrays Capture photons Biological imaging with photons widespread Can we be more direct? Imaging with ions Build CMOS imaging arrays for protons Functionalise post-fabrication

21 Starting point The ISFET It s a proton sensor (proton = H + ph) Need array version

22 Interface Electronics Column of pixels Addressable elements S/D follower Readout circuitry Decoding and multiplexing

23 Implementation Foundry technology. Standard 0.35 µm CMOS process Access via Europractice IC service Cross-section through ISFET. Passivation Via holes Polysilicon Metal 3 Metal 2 Metal 1 W/L = 1/0.35 µm

24 Packaging Encapsulation Micrograph Cloning ring.

25 Threshold Voltage Modification Test circuit Pixel layout Effect of UV exposure 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

26 Surface Topography 2 x 2 array 16 x 16 array Step height: 600 nm Pixel: 3 x 6 µm 2 Spacing: 10 µm Frame border Pixel: 11.6 x 11.6 µm 2 Spacing: 0.6 µm

27 Glycolysis Bioassay Example pixel Sensor array Decrease in ph due to lactate (before addition of glycolysis inhibitor) and CO 2 diffusing out of cells into medium Increase in ph due to vanishing [H + ] in micro-environment between cells and sensor array surface

28 Summary Diverse range of technologies under investigation Leveraging biotech out of well-established microelectronics technology The technology is reasonably mature Opportunities for biochemists to explore