Case Studies in MEMS Case study Pressure sensor

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Case Studies in MEMS Case study Pressure sensor Technology Bulk micromach. + bipolar circuitry

Case Studies in MEMS Case study Pressure sensor Technology Bulk micromach. + bipolar circuitry Transduction Packaging Piezoresistive sensing of diaphragm deflection Plastic Accelerometer Surface micromach. Capacitive detection of proof of mass motion Metal can Electrostatic projection displays Surface micromach. + Xe. F 2 release Electrostatic torsion of suspended tensile beams Glass bonded

Optical MEMS Why are MEMS used here? - Structures are the same dimensions as

Optical MEMS Why are MEMS used here? - Structures are the same dimensions as the wavelength - Small displacement has a large effect, can be used for SWITCHING * Interferometric devices * Scanning devices - A photon has no mass, easy to deflect light -Can fabricate large-scale systems, (e. g. 1000 X 1000 displays as in the Digital Micro-mirror device) Courtesy: H. Toshiyoshi

Applications of Electrostatic projection displays Courtesy: H. Toshiyoshi

Applications of Electrostatic projection displays Courtesy: H. Toshiyoshi

Applications of Electrostatic projection displays Control of light through: (1) Reflection : Texas Instruments

Applications of Electrostatic projection displays Control of light through: (1) Reflection : Texas Instruments (DMD: Digital Micromirror Device) (2) Diffraction: Silicon light Machines (GLV: Grating Light Valve)

Texas Instruments’ Digital Micro-mirror Device (DMD) The most advanced display technology to date -

Texas Instruments’ Digital Micro-mirror Device (DMD) The most advanced display technology to date - Each rotatable mirror is a pixel - 1024 shades of gray and 35 trillion colors possible - use in projection systems, TV and theaters

Distinguishing features of a DMD • Gray scale achieved by digital and analog modulation

Distinguishing features of a DMD • Gray scale achieved by digital and analog modulation - Digital: Pulse Width Modulation (PWM) - Analog: Spatial Light Modulation (SLM) • Compact, low weight and low power Portable system H. Toshiyoshi • Higher brightness and contrast

History (1): Si cantilever based light modulator Petersen, K. E. , “Micromechanical light modulator

History (1): Si cantilever based light modulator Petersen, K. E. , “Micromechanical light modulator array fabricated on Silicon”, Applied Physics Letters, 31, pp. 521 -523, 1977 • Electrically actuated, individually addressable cantilevers • Pull -in • Si. O 2 structural layer • Si sacrificial layer

History(2): Torsional electrostatic light modulator Petersen, K. E. , “Silicon torsional scanning mirror”, IBM

History(2): Torsional electrostatic light modulator Petersen, K. E. , “Silicon torsional scanning mirror”, IBM Journal of Research & Dev. , 24, pp. 631 -637, 1980 • Electrically actuated torsion mirrors • 1012 cycles, with ± 1 o rotation • Bulk micromachining of Silicon

History (3): Deformable Mirror Devices L. Hornbeck, “Deformable Mirror Spatial Light Modulator”, SPIE, vol.

History (3): Deformable Mirror Devices L. Hornbeck, “Deformable Mirror Spatial Light Modulator”, SPIE, vol. 1150, p. 86, 1989 Elastomer based Cantilever based Membrane based Torsion: Amplitude dependent modulation Cantilever based: Phase dependent modulation

Digital Micro-mirror device www. dlp. com

Digital Micro-mirror device www. dlp. com

DMD Fabrication (6 photomask layers) DMD superstructure on CMOS circuitry • Surface micromachining process

DMD Fabrication (6 photomask layers) DMD superstructure on CMOS circuitry • Surface micromachining process • Hinge: Aluminum alloy (Al, Ti, Si) (50 -100 nm thick) • Mirror: Aluminum (200 -500 nm thick) • Aluminum : structural material • DUV hardened photoresist: sacrificial material • Dry release (plasma etching) reduces stiction Courtesy: H. Toshiyoshi

Texas Instruments DMD characteristics

Texas Instruments DMD characteristics

Digital Micro-mirror device www. dlp. com

Digital Micro-mirror device www. dlp. com

Principle of Operation Balancing electrical torque with mechanical torque Telectrical is proportional to (voltage)2

Principle of Operation Balancing electrical torque with mechanical torque Telectrical is proportional to (voltage)2 Tmechanical is proportional to (deflection, a) a

Electrostatic model of a torsion mirror Arc length Electric field x r q a

Electrostatic model of a torsion mirror Arc length Electric field x r q a Mirror d V Torsion beam -Neglect fringing electric field -Neglect any residual stress

Electrostatic model of a torsion mirror Electrostatic torque (Telec) = Mechanical torque (Tmech) =

Electrostatic model of a torsion mirror Electrostatic torque (Telec) = Mechanical torque (Tmech) = e. g. polysilicon, G = 73 GPa r= 2. 35 g/cm 3 x r q a Mirror d V Torsion beam W: width L: length t: thickness

Balancing electrical and mechanical Torques Graph Courtesy, M. Wu

Balancing electrical and mechanical Torques Graph Courtesy, M. Wu

Operation of torsion mirror based DMD

Operation of torsion mirror based DMD

DMD bias cycles

DMD bias cycles

Energy domain model The torsion mirror as a capacitive device

Energy domain model The torsion mirror as a capacitive device

Calculation of capacitance From: M. Wu and S. Senturia

Calculation of capacitance From: M. Wu and S. Senturia

Approximate solution - stable angle and pull-in voltage From: M. Wu and S. Senturia

Approximate solution - stable angle and pull-in voltage From: M. Wu and S. Senturia

Schemes of Torsion Mirror operation Pull-in voltage Single side drive x r a q

Schemes of Torsion Mirror operation Pull-in voltage Single side drive x r a q Scan angle Angle-voltage Low Small Non-linear High Large Linear d V Push-pull drive x r d a q V+v Bias voltages V-v

Digital Micro-mirror Device (Texas Instruments)

Digital Micro-mirror Device (Texas Instruments)

1 -DMD chip system - Can create 1024 shades of gray - used in

1 -DMD chip system - Can create 1024 shades of gray - used in projectors, TVs and home theater systems

2 -DMD chip system - Can create 16. 7 million shades of color -

2 -DMD chip system - Can create 16. 7 million shades of color - used in projectors, TVs and home theater systems

3 -DMD chip system is used for higher resolutions -For movie projection and other

3 -DMD chip system is used for higher resolutions -For movie projection and other high end applications (35 trillion colors can be generated)

Courtesy: M. C. Wu Grating Light Valve (GLV) - Silicon Light Machines (www. siliconlight.

Courtesy: M. C. Wu Grating Light Valve (GLV) - Silicon Light Machines (www. siliconlight. com) Reflection : broad band Diffraction : Wavelength (l) dependent 1 mirror/pixel (2 -D array) 6 ribbons/pixel (1 -D array) Larger displacements (msec time response) Displacement: l/4 (nanosecond response) Voltage controlled A fixed angle Constant intensity Diffracted intensity varied by voltage

Mode of Operation A diffraction grating of 6 beams 1 pixel

Mode of Operation A diffraction grating of 6 beams 1 pixel

1 pixel in the GLV: 6 ribbons wide

1 pixel in the GLV: 6 ribbons wide

By using a different spacing between ribbons, one can create different color-oriented pixels

By using a different spacing between ribbons, one can create different color-oriented pixels

MEMS in Optical Communications - Very quick switching (> 100 k. Hz), low losses,

MEMS in Optical Communications - Very quick switching (> 100 k. Hz), low losses, - Low cost, batch fabrication 1 X 2 Optical switch Optical fibers Optical Micro-mirrors used with Add-Drop multiplexers Bell Labs research

MEMS Micro Optical Bench Integrable Micro-Optics MEMS Actuators Opto MEMS Slide courtesy: H. Toshiyoshi

MEMS Micro Optical Bench Integrable Micro-Optics MEMS Actuators Opto MEMS Slide courtesy: H. Toshiyoshi

Scratch Drive Actuator Akiyama, J. MEMS, 2, 106, 1993 - Large total displacements can

Scratch Drive Actuator Akiyama, J. MEMS, 2, 106, 1993 - Large total displacements can be achieved (1 mm) @ 100 Hz – 100 KHz - Increments / forward movement as small as 10 nm - voltages required are large Scratch actuator movement Voltage applied

MEMS in 3 -dimensions “Microfabricated hinges”, K. Pister et al, Sensors & Actuators A,

MEMS in 3 -dimensions “Microfabricated hinges”, K. Pister et al, Sensors & Actuators A, vol. 33, pp. 249 -256, 1992 -Assembly of three-dimensional structures - Large vertical resolution and range Surface micromachining based Other variants of the hinge H. Toshiyoshi

MEMS in Optical Communications - Very quick switching (> 100 k. Hz), low losses,

MEMS in Optical Communications - Very quick switching (> 100 k. Hz), low losses, - Low cost, batch fabrication 1 X 2 Optical switch Optical fibers Optical Micro-mirrors used with Add-Drop multiplexers Bell Labs research