CNT-BASED THERMAL CONVECTIVE ACCELEROMETER Presented by Yu ZHANG. Supervised by Prof. Wen J. LI

O UTLINE Introduction Literature Review Sensor Design Test Setup Test Results Conclusion 2

INTRODUCTION Literature Review Sensor Design Test Setup Test Results Conclusion 3

I NTRODUCTION  Background  The method to align post grown Carbon-Nanotubes between microelectrodes using dielectrophoretic (DEP) forces was developed in CMNS  Experiments showed CNT bundles can detect environmental temperature change  When heated within liquid, CNTs can generate thermal vapor bubble around itself

I NTRODUCTION  Idea  Acceleration/tilting will lead to deformation of the vapor bubble.  Temperature distribution around the bubble will change  If other CNT bundles can be fabricated around the bubble, they can sense the temperature change caused by acceleration. 5

I NTRODUCTION  Aim of Research CNT-based thermal accelerometer Review the working principle of thermal motion sensor Choose applicable principle, design the structure Fabricate sensor chips, build prototypes Purchase and set up test equipments Test and characterize sensors’ response 6

LITERATURE REVIEW Introduction Sensor Design Test Setup Test Results Conclusion 7

L ITERATURE R EVIEW 8  Literature Review: Contents  Motion Sensors  Thermal Motion Sensors  Carbon-Nanotube Manipulation  Carbon-Nanotube Sensors

L ITERATURE R EVIEW  Review of Motion Sensors  Convert motion into electric signal Linear motion: accelerometer/inclinometer Angular motion: gyroscope  Application in industry, consumer electronics, input devices, instruments Inclination: automobile stability, platform stabilization Orientation: gesture recognition, inertial navigation, active control Vibration: active suspension system, machine noise detection Shock: air bag system, release systems, structure monitoring 9

L ITERATURE R EVIEW  Piezoresistive  Conventional Motion Sensors  Piezoelectric  Capacitive 10 Acceleration Moving/bending of solid structure Change of detector output Convert to electric signal

L ITERATURE R EVIEW  Pros  Easy to design and model  Standard IC process *  Good cost/performance ration  Fast response  Cons  Rely on solid moving parts: proof mass  Better sensitivity requires bigger proof mass  Fragile, cannot measure large acceleration (<20g)  Low shock survival rate 11 * for surface micromachined sensors only Acceleration Move/bending of solid structure Change of detector output Convert to electric signal replacement for this step?

L ITERATURE R EVIEW  Thermal convective motion sensor  Details  Acceleration will lead to forced convection of liquid within sealed chamber  Use flow sensors to detect the flow speed caused by convection 12 Acceleration Convection of liquid Change of detector output Convert to electric signal Figure from [6]

L ITERATURE R EVIEW  Anemometer  Micro Flow Sensors  Calorimetric flow sensor  Time-of-flight flow sensor 13  Based on thermal phenomenon: Add local heat to fluid, measure the resulting temperature Very small Reynolds Number Laminar flow heat transfer Three sensing methods

L ITERATURE R EVIEW  Research on Thermal Convective Accelerometer  First reported in 1997  Research groups in Canada, US, France, Germany, China.  Commercial products by MEMSIC. Inc.  Based on integrated thermal flow sensor, to sense convection caused by acceleration.  Up to two sensing axis 14 AccelerationConvection of liquidThermal detectorConvert to electric signal

L ITERATURE R EVIEW  Working Principle  One-axis Structure  Two-axis Structure 15 Figure from….

L ITERATURE R EVIEW  Carbon-Nanotubes  Allotropes of carbon with a cylindrical nanostructure  Single-walled and Multi-walled  Synthesis method: arc discharge, laser ablation, chemical vapor deposition 16  CNT Integration  Selectively grow on desired position  In situ CVD  Manipulate post-grew CNTs  Use AFM tips to move  Fluid friction  Dielectrophoretic (DEP) force

L ITERATURE R EVIEW  Review of CNT Sensors  Mechanical sensors, chemical sensors, thermal sensors, pressure sensors  Sensing method: Raman spectrum shift Performance change as circuit elements Resonators Transistors Resistance change Deformation Temperature Chemical reaction 17 Possible for micro sensors Reported by CMNS and other research groups

 Literature Review: Conclusion  Build the sensor upon thermal convection sensing principle  Follow and improve the DEP manipulation method  Deposited CNT bundles work as Temperature Detectors 18

SENSOR DESIGN Introduction Literature Review Test Setup Test Results Conclusion 19

20  Sensor Design: Contents  Important Questions  Mask Design  Fabrication  Sensor Prototyping

S ENSOR D ESIGN  Important Design Questions  Project requirement consideration The structure should be DEP compatible Sensing structure: Anemometer Calorimetric structure Time-of-flight structure No conditioning and feedback circuit  MEMS structure consideration Thermal insulation 21 selected structure

S ENSOR D ESIGN  Thermal Insulation  Where to insulate (minimize heat flux) Between heater and detectors Between the sensing block and the substrate  Better thermal insulation leads to Higher heater temperature Better sensitivity 22

S ENSOR D ESIGN  Benefits of Thermal Insulation 23 substrate flow Q T detector T substrate > T detector brings away heat R detector heat from substrate Better thermal insulation Minimize heat capacitance of the substrate Reduce heat flux from substrate Improve sensitivity

S ENSOR D ESIGN  Bridge Structure  Insulation Layer  Etched Cavity  Membrane 24 Top view Side view

S ENSOR D ESIGN  Thermal Insulation Design MaterialSiliconPorous SiliconGlassAir κ (Wm -1 K -1 )1251.1* Use glass as substrate  Good thermal insulation result  Fabrication process available  Simple structure  Need Cr layer to improve adhesion  Cannot integrate with IC * From Reference [12]

S ENSOR D ESIGN  Sensor Chip Mask Design  Mask Layout  Sensing Block 26  One pair of electrodes -> anemometer structure One CNT bundle as heater/detector  Three pairs of electrodes -> calorimetric structure (1-axis) One CNT bundle as heater, two as detectors  Five pairs of electrodes -> calorimetric structure (2-axis) One CNT bundle as heater, four as detectors One 1-axis calorimetric structure Three anemometer structure

S ENSOR D ESIGN  Sensor Chip Fabrication 27

S ENSOR D ESIGN  CNT Manipulation  Multi-walled CNTs are used  Disperse MWNT into ethanol  Separate bundles using ultrasonic  Drop 2μL above the electrodes  Apply 8V peak-peak, 1MHz AC, from signal generator  Improved DEP Circuits  Captured Microscope Image 28

S ENSOR D ESIGN  Sensor Building Processes 29

S ENSOR D ESIGN  Prototypes 30

TEST SETUP Introduction Literature Review Sensor Design Test Results Conclusion 31

T EST S ETUP  Source and Measure  Test Circuit  Source meters 32  Use Source & Measure Units (SMUs) to power up and measure. Keithley 2400 Sourcemeter: 1 SMU Keithley 2600 Sourcemeter: 2 SMUs  Sourcemeters linked together to computer via GPIB  Sourcemeter data synchronized by collected time stamps  Constant current configuration

T EST S ETUP  Tilting Plate  Test Setup  Vibration Exciter  Test Setup 33

TEST RESULTS Introduction Literature Review Sensor Design Test Setup Conclusion 34

T EST R ESULTS 35  Test Results: Contents  Thermal Sensing Test  Tilting Test  Vibration Test

T EST R ESULTS  Thermal Sensitivity  Tested in Climatic Chamber. Fixed humidity.  Higher temperature -> Smaller resistance: Negative TCR 36

T EST R ESULTS  Self-heating Test 37

T EST R ESULTS  Temperature Change Caused by Heater 38

T EST R ESULTS 39  Test Results: Contents  Proving Test  Tilting Test  Vibration Test

T EST R ESULTS  Tilting Test  Tested on tilting plate Anemometer structure with air sealed: No response Anemometer structure with liquid sealed: No response Calorimetric structure with air sealed: No response Calorimetric structure with liquid sealed: 40

T EST R ESULTS  Tilting Test  Configuration Convection medium: ethanol Input power heater: 6μW detectors: 1nW each  Result Two sensors give opposite responses. Very good sensitivity. Very small power consumption Liquid convection medium 41 Conventional thermal accelerometers: 0.2mW to 480mW* *Table 2.2, Page 24, Thesis

T EST R ESULTS 42  Test Results: Contents  Proving Test  Tilting Test  Vibration Test

T EST R ESULTS  Vibration Exciter Calibration  Use laser vibrometer to measure velocity, then calculate acceleration  Fixed input power, varying input frequency. Frequency limited by Sourcemeter sampling frequency 43

T EST R ESULTS  Vibration Test Result  Test progress Anemometer structure with sealed air: yes Anemometer structure with sealed liquid: no Calorimetric structure: no 44

T EST R ESULTS  Sensor Response to Vibration  Test mode: bias current 10nA  Power consumption: 45

T EST R ESULTS  Sensor Response Under Different Heating Current  Frequency fixed to 2Hz  Input current: 10pA to 0.1mA  Response defined by 46 In tests, driven current was set to 10nA

T EST R ESULTS  Acceleration Responsivity  More sensitive to small acceleration  Linear – log relationship  Saturation limit > 1.2m/s 2 47

T EST R ESULTS  Phase Delay Test  180 ° phase delay  Response time not detectable 48 Dual channel Sourcemeter Dual channel Sourcemeter velocity Laser Vibrometer Sensor voltage output a=dv/dt R=vi

CONCLUSION Introduction Literature Review Sensor Design Test Setup Test Results 49

C ONCLUSION  Conclusion – Work Done  Working principle, structures and performances of currently developed thermal convective accelerometers were reviewed.  CNT-based thermal convective accelerometers were designed and prototyped.  Testing facilities were purchased and set up.  Prototypes were tested under inclination and vibration. 50

C ONCLUSION  Conclusion - Results  Calorimetric structure with sealed ethanol can sense static inclination  Anemometer structure with sealed air can sense vibration  Contributions First CNT based motion sensor First CNT based thermal convective motion sensor Smallest power consumption * No solid proof mass, easy to fabricate More understanding about heating and sensing effect of CNTs 51 * Considering the sensing block only

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SUPPORTING MATERIALS 53

S UPPLEMENTS  Improving Frequency Test Range 54 sourcemeter sampling limit vibration exciter working range 1Hz10Hz100Hz1000Hz0.1Hz0.001Hz New circuit sampling limit 1Hz10Hz100Hz1000Hz0.1Hz0.001Hz vibration excitercrank-link mechanism

S UPPLEMENTS  Crank-link Mechanism 55

S UPPLEMENTS  Sensor Read-out Circuit 56

S UPPLEMENTS  Future work – Sensor Charactorizaiton  Step response  Bandwidth (frequency response)  Saturation (requires higher acceleration peak) 57

 Future Work – Sensor Design  Size of sealed chamber  Noise level  Optimized input current (sensitivity and noise)  Properties of convection medium (liquid, air, pressure)  Compensation of environmental temperature change  Feedback control 58