MEMSA Platform For Augmented Reality

Sandro Dalle FesteAnalog MEMS & Sensor Product GroupProduct Development ManagerSTMicroelectronics

23 September, 2014Milan

• A global semiconductor leader

• The largest European semiconductor company

• 2013 revenues of $8.08B

• Approx. 45,000 employees worldwide

• 12 manufacturing sites

• Listed on New York Stock Exchange, Euronext Paris and BorsaItaliana, Milano

Who we are

As of December 31, 2013

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Where you find us

Our automotive products are making driving safer, greener and more entertaining

Our smart power products are allowing our mobile products to operate longer and making more of our energy resources

Our MEMS & Sensors are augmenting the consumer experience

Our Microcontrollers are everywheremaking everything smarter and more secure

Our digital consumer products are powering the augmented digital lifestyle

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MEMSA Platform For Augmented Reality

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MEMS: Not just Motion & Environmental Sensors… 5

• Piezoelectric MEMS nozzles for Industrial Printers

• Piezoelectric MEMS lens

• MEMS Speakers

• MEMS µ-Mirrors for Pico-projectors

…. But Also Actuators 6

MEMS for Sensing and Actuating 7

Sensors

Micro-actuators

Physical change

Signal

MEMS

Mechanical Electric

Motion Environmental

Optical Micro-actuators

FluidicMicro-actuators

Audio

Electro

Mechanical

The Human Machine Interaction Evolution

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2000Success thank to

smartphones, tablets and interactive panels

1987From a technical

paper

1968Mouse First Patent

1990On the mass market

A Growing Ecosystem driven by Applications

• Gesture Recognition

• Facial Recognition

• Mood Identification

• Avatar

• 3D Distance Camera

• 3D Rendering

• Driver Drowsiness Detection

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What is behind? 10

MEMS MIRROR

System Overview: Time of Flight 11

Depth (distance) captured by reflected wave phase

System Overview: Structured Light 12

Evaluate Depth from ray-plane triangulation1

Multiple line scan2

Accurate, effective but

visible

System Overview: Structured Light 13

Binary coded pattern3

Line code-word : 1010010

Pattern 1

Pattern 2

Pattern 3

…

Accurate, effective, IR can be used

The System Core: MEMS Mirror 14

• Mechanical structure designed to work in torsional mode for reflected beam angular deflection.

• Electrostatic actuation and opening angle sensing via comb drive electrodes.

• Metallization material chosen to maximize reflection in requested working optical wavelength range (typically Au for IR and Aluminum for visible light).

Stator comb drive electrodes (actuation

and sensing) Torsional spring

Reflecting metallization

Rotor comb drive

electrodesRotor mass

Working principle: Electrostatic Actuation

• Electrostatic force is used as actuation mechanism by means of a comb drive structure, i.e. interdigitated silicon fingers, which apply a torqueing moment on the MEMS.

• Capacitance change in comb drive is also used for opening angle detection.

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Comb drive rest capacitance:

Comb drive forcing moment:

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V

Electrostatic torque on mirrorstructure

Actuation configuration & Modes of operation

• Depending on the application, resonant or quasi-static operation or both could be required. Different comb drive configurations can be implemented to reach the desired behavior.

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In-plane comb fingers for resonant mode operation

Out-of-plane comb fingers for quasi-static mode operation

Handle with cavity to allow mirror movement

Mechanical structure layer

Resonant layout Example 17

substrate pads

comb driveTorsion hinges

Reflecting surface

Closed loop operation• Both resonant and quasi static mirrors need a closed loop driving:

• Resonant mirror needs a phase locking algorithm to assure a very high stability in max tilting angle and sinusoidal motion

• Quasi static mirror, which is actuated with a saw-tooth wave, needs a self-resonance cancellation algorithm to avoid artefacts on the projection

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ScanLine

RetracePhase locking @ the max of the angle-frequency curve

Resonant Mirror Motion Quasi Static Mirror Motion

Time

Next Step: Piezo actuation ?

Thank You