EE143 F2010 Lecture 25 Capacitive sensors Typically used to measure displacement C e0 A d Area A Separation d Example Pressure Transducer Professor N Cheung U C Berkeley C x C x P 1 EE143 F2010 Lecture 25 CO Microsensor Process Flow Source http www itri org tw mems Professor N Cheung U C Berkeley 2 EE143 F2010 Lecture 25 MEMS Mechanical Switch Source Drain Gate s Drain Contact Areas 0 4x0 4 um2 to 8x8 um2 Devices from 50 um to 250 um long Professor N Cheung U C Berkeley EE143 F2010 Lecture 25 Mechanical Switch Process Flow Elec0 Layer Isolation Si Substrate Pre alignment Pattern Elec0 Isolation Growth 6000A Low Temp Oxide 1000A Stoichiometric Silicon Nitride Main Sacrificial LTO Poly 0 Deposition Poly 0 Formation RIE to isolation w overetch Main Sacrificial Deposition 5500A Low Temp Oxide Dimple hole Dimple Formation DRIE to Isolation or timed DRIE Professor N Cheung U C Berkeley EE143 F2010 Lecture 25 Mechanical Switch Process Flow Fine refill sacrificial HTO Fine Sacrificial Deposition 650A High Temp Oxide Anchor holes Anchor Formation DRIE to isolation layer Elec1 Layer Sacrificial Release Poly 1 Deposition 5500A 615C n doped Poly 1 Formation RIE etch to Main Sac Sacrificial Release HF HCl 20 then critical pt dry Process Finished Professor N Cheung U C Berkeley EE143 F2010 Lecture 25 Example of Thermal Bimorph Actuator gold 14 x 10 6 oC Professor N Cheung U C Berkeley Si 2 6 x 10 6 oC 6 EE143 F2010 Lecture 25 Process Flow of Micro tweezers by selective CVD Tungsten 0 volts open Professor N Cheung U C Berkeley 15 volts closed 7 EE143 F2010 Lecture 25 Process Flow of MEMS Rotating Mechanisms In Plane Movement Micro turbine Engine Professor N Cheung U C Berkeley 8 EE143 F2010 Lecture 25 Example Lateral Resonator Professor N Cheung U C Berkeley 9 EE143 F2010 Lecture 25 Paschen Curve for gas breakdown Using electrostatic actuator convenient voltage is limited to 200V Professor N Cheung U C Berkeley 10 EE143 F2010 Lecture 25 Electrostatic Gated Pneumatic Valve Professor N Cheung U C Berkeley 11 EE143 F2010 Lecture 25 Process Flow of Electrostatic Gated Pneumatic Valve Professor N Cheung U C Berkeley 12 EE143 F2010 Lecture 25 SCREAM Process Question Why 2nd Si etch Al electrodes Professor N Cheung U C Berkeley 13 EE143 F2010 Lecture 25 Monolithic MEMS IC Integration Approaches Interleaved process Processing steps for MEMS and IC are interleaved in the process flow Modular process Allows for separate development optimization of MEMS and electronics components Use of IC and or MEMS foundries a possibility Professor N Cheung U C Berkeley 14 EE143 F2010 Lecture 25 Challenges of Modular processes MEMS first Approach Topography is an issue Degradation of MEMS devices during hightemperature IC process steps Electronics must be protected during HF release etch IC first Approach MEMS must be low temperature process Electronics must be protected during HF release etch Professor N Cheung U C Berkeley 15 EE143 F2010 Lecture 25 Interleaved Process Example Analog Devices Inc Metallization process steps performed last Performance of MEMS and electronics compromised Professor N Cheung U C Berkeley 16 EE143 F2010 Lecture 25 MEMS first Process Example Sandia National Lab MEMS fabricated in 12mm deep trench Filled with SiO2 and planarized using CMP Modular process but IC foundries wary Professor N Cheung U C Berkeley 17 EE143 F2010 Lecture 25 MEMS Last Process Example UC Berkeley Non standard refractory W metallization melting point 3000oC IC foundries not interested Professor N Cheung U C Berkeley 18 EE143 F2010 Lecture 25 New MEMS Last Technology A Franke UC Berkeley Standard CMOS process Al based metallization Poly SiGe as structural material processing temperatures 500 C possible Amorphous Si protects CMOS during HF release etch Professor N Cheung U C Berkeley 19 EE143 F2010 Lecture 25 MEMS Last Sensor The cavities are formed after formation of the lower electrode when a thick SiO2 layer and the upper electrode are deposited In the upper electrode multiple holes are etched a plasma or wet etchant for SiO2 is applied through the holes to attack the thick SiO2 layer the SiO2 under the holes is removed and small cavities of SiO2 are formed and connected gradually Finally the connected cavities produce a large cavity under the upper electrode The final cavity size depends on the hole size and etching conditions including time gas flow rate and gas components Source Hitachi 2009 Professor N Cheung U C Berkeley 20 EE143 F2010 Professor N Cheung U C Berkeley Lecture 25 21 EE143 F2010 Lecture 25 DNA analysis in Microchannels Stretching DNA and sequencing Cao et al Princeton Entropic trap Han Craighead Cornell MIT 75nm 30 m 30 m Professor N Cheung U C Berkeley 22 EE143 F2010 Lecture 25 Optical observation of single molecules in their natural state Cornell Univ Light impeding Al holes Zero mode waveguides Professor N Cheung U C Berkeley 23 EE143 F2010 Lecture 25 Responsive Drug Delivery Systtem Professor N Cheung U C Berkeley Source Madou Lab Chip 3 26 28N 2003 24 EE143 F2010 Lecture 25 Heterogeneous Integration of Microsystems Professor Nathan Cheung EECS For reference only BioMEMS Emitters Filter Detectors GeOI Green LED Si Ge Low Power CMOS CPU Blue LED MOS IC III V Encapsulated battery with switch LED 5mm 200 mm Micro LED display pump Laser Array Laser Emitter Arrays Spectrometer Optical Micro mirrors Modulator Micro fluidic channels InGaN LEDs on Si Encapsulated Power source 1mm Professor N Cheung U C Berkeley Si microfluidic channels 200 mm 25 EE143 F2010 Lecture 25 Summary of MEMS Processing Module Stress Strain Young s Modulus Poisson Ratio Yield Stress Thin film stress intrinsic thermal expansion external Substrate warpage calculations Stoney s Equation Stiction problems and solutions Bonding and Molding qualitative Principle of MEMS sensing and actuation qualitative Given a MEMS structure design the process flow MEMS CMOS Integration Sequence Interleaved MEMS first MEMS last Professor N Cheung U C Berkeley 26
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