SPR (Surface Plasmon Resonance) Chemical Sensing Microsystems
Distributed Microsystems Laboratory Integrated Interface Circuits for Chemiresistor Arrays Carina K. Leung* and Denise Wilson, Associate Professor Department of Electrical Engineering University of Washington *Now with Intel, Dupont Washington Integrated Interface Circuits for Chemiresistor Arrays Outline Project Description (High Density Chemiresistor Arrays) Chemiresistor Background Project Context Circuit Approach 1: Differential Measurement of Resistance Circuit Approach 2: Resistance-to-Frequency Conversion
Comparison of Approaches Summary Acknowledgements Project Description Popular approach to chemical sensing (traditional) Small number (highly selective) sensors in an Application targeted to 1-2 analytes In an understood background Another approach to chemical sensing (olfactory)
Large number (broad, overlapping selective) sensors in an Application targeted to many analytes And their (many) interferents In a cluttered and complicated background Candidates for high density arrays of chemical sensors are few: Require small size, linear operation, broad selectivity, compatibility with integration, and room temperature operation Chemiresistor Background Composite polymer chemiresistors Conductive Element (such as carbon black) combined with
Chemically sensitive element (polymer) Basic operation Polymer swells in response to target analytes Conductive particles move farther apart (conductivity increases) Linear response at low concentrations R-Ro = Ro (k) [C] Ro= baseline resistance (large and highly variable) [C] = analyte concentration Superposition can be applied to multiple analytes presented simultaneously
Project Context High resolution Sensor Arrays Require Integration Circuits produced in CMOS Gold post-deposited electrochemically Sensor coating sprayed on gold 1-2 layers of metal required for sensor Challenge: Design processing circuits that Ignore large, variable baseline resistance Amplify very small changes in polymer resistance on top of large baselines
Conform to VLSI footprint that addresses: Electrode Geometry Required sensor density Circuit performance Circuit Approach #1 Differential Approach On-chip chemiresistor divided into: One chemically sensitive resistor One or (three) reference resistors Passivated (responsive to zero analytes) or
Exposed, not functionalized (responsive to all analytes) Resistive Bridge is part of sensor Remaining circuits are designed for maximum gain under constrained footprint (= sensor platform) Circuit Approach #1 Differential Approach Resistive Bridge output transferred to: Differential Amplifier Comparator with ramping input for serial A/D conversion Vdd
Rbias Differential Amplifier: maximum gain in small footprint Comparator: fully serial (simple) A/D conversion acceptable because of slow sensor response time Rbias + - Design constraints: Vdd RSensor RBaseline + - Out Circuit Approach #1 Differential Approach
Circuit Gain 20 (Differential Amplifier) -20 (Comparator) Sensor Performance: Bridge approach eliminates effect of broad range in baseline on circuit gain However, additional bias resistors add more noise (electrical and transduction) Translation: 25V detection limit Independent of baseline
0.01% (R) detection limit and resolution Circuit Approach #2 Resistance to Frequency Conversion Sensor platform contains three terminals: Outer ring terminals shorted together outside sensor platform to enable circuits to fit underneath Allows a single resistor per platform for chemical sensing More active area (fill factor) than previous approach. Electrode geometry more readily optimized for best noise performance. Circuit Approach #1 Resistance to Frequency Conversion Operation:
Sensor resistance charges Co As the capacitor charges, it trips the Schmitt trigger, causing the feedback to discharge the capacitor The frequency of the charge/discharge cycle becomes smaller with increasing resistance (smaller current) Hysteresis reduces impact of noisy sensor response Out C RSensor Co C Schmitt Trigger Circuit Approach #2
Resistance to Frequency Conversion Sensitivity: Baseline (730k) = .12%/ Baseline (9.26k) = 4.1%/ Resolution/Detection Limit: Change in resistance from baseline Baseline (730k) = .07% Baseline (9.26k) = .02% Comparison
Both circuits fit underneath sensor platform (.04 mm2 area) Fill Factor: Approach #1: 25% Approach #2: close to 100% (with exceptions for metal routing) Sensitivity: Approach #1: 400 (V/V) Approach #2: between .12%/and 4.1%/ Resolution/Detection limit: Approach #1: .01% change in resistance Approach #2: between .02% and .07% Other: Approach #2: more resilience to fluctuations in response due to built in hysteresis.
Summary We have designed and fabricated two circuits for processing the response of composite polymer chemiresistors. Performance enables sub-ppm detection of many common analytes, while having having zero impact on sensor area. Acknowledgements The authors would like to thank Nathan Lewis and his graduate group at the California Institute of Technology for data and technical assistance, as well as a subcontract through CalTech on ARO Grant DAAG55-98-1-0266.
This slide introduces the key themes of safeguarding. By clicking on each door - this will take you to a more detailed explanation of the issue. Within the theme 'Child abuse', physical, emotional, sexual abuse and neglect will be covered....
of near-Earth IMF, B, solar wind speed, V. SW, and the Open Solar Flux (OSF), F. S the minima in annual mean V. SW. at 1878 and 1900 are only slightly greater than the lowest hourly means in the satellite...
What types exist? Can they be reintroduced? Disturbance Regimes in Michigan Mack Lake Fire, 1980 First 6 hours 1 human life 44 homes 20,000 A After 30 hours, fire contained within 24,000 A area Are disturbance regimes evident in Michigan...
The game of football is the oldest of all the English national sports. Football has been played in one form or another for hundreds of years. First it was a very rude game. This game is believed to have descended...
Arial Black Arial Times New Roman Symbol Wingdings JDM00002 Microsoft Office Excel Chart Arc Spray Systems BP-400 BP-400 Model 8830MHU "The System Which Defined TAFA" 8830MHU Model 8835MHU 8835MHU ArcJet Spray Attachment "CoArc™" 9935 Spray System Features CoArc Options 9935...
Generalized Tonic Clonic Seizure … there is a mild generalized tremor, which is, in effect, a repetitive relaxation of the tonic contraction. … begins at a rate of 8 per second and coarsens to 4 per second; then it rapidly...
Introduction to Photography. This is a camera. On/Off Switch. Rather Important…. Mode Wheel. It should be on Manual. ;D. Shutter Release Button. Press down halfway to focus, and fully to take the picture. ... Canon Nikon. F-Stop Control Button.
Hazlems Fenton LLP . Chartered Accountants. London. Doing Business in the United Kingdom. Business entities. Business administration. Taxation. Corporate taxes. Personal income taxes. Withholding taxes and double tax treaties. International aspects. Other taxes.
Ready to download the document? Go ahead and hit continue!