MEMS in Cameras

Vijay Chandrasekharan / Eric Tosaya 5/21/2014

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Camera Evolution • Evolutionary Challenges

• Miniaturization • Robustness (Drop test) • Photography for everyone • Rough handling conditions (Moisture) • Low cost

• Driving required Innovations • Packaging (integration) • Lens design • Actuator

• Autofocus • Image Stabilization • Zoom

• Imaging software (large pixel data) http://www.acme-ug.org/wp-content/uploads/2013/09/Evolution-of-the-camera.jpg

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FUTURE VISION: DSC functionality+ in smartphone via mems|cam

13MP+ Camera Module Autofocus (available) Computational Imaging (available) Image Stabilization (possible) Shutter (available) Motion Sensing (available) Optical Zoom

Digital Still Cameras Nikon Coolpix DSC (55x33x14 mm)

Motor Driven Autofocus and Zoom

Voice coil image stabilization

Voice coil shutter

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GEN2 AF MEMS Device

1mm

GEN3 AF MEMS Device

1mm

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Prototype lens barrels with MEMS OIS (Optical Image Stabilization) actuator are functional.

Patents filed for new concept Gen4 MEMS actuator

MEMS OIS actuator

Image Stabilization

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World’s smallest AF cameras Supports 6.5 mm in x-y and no added z height

Actuator is integrated inside the camera’s lens barrel

MEMS AF Camera

MEMS AF Actuator

MEMS Characteristics Payload – 4 mg (> O[102] for other MEMS) Motion – 100 um (~O[102] for other MEMS) Shock – >10000 g shock survivability in a smartphone

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• MEMS actuator is based on a comb drive • Comb drives are capacitive actuators that utilize electrostatic forces that act between two electrically conductive

combs • Combs are arranged so they never touch • When voltage is applied, it causes the combs to be drawn together, causing movement • The force (and movement) is proportional to the change in capacitance (and voltage applied) between the combs

Electrostatic actuation and position sensing. Ultra- low power.

MEMS Actuator Principle

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dE dCF Vds ds

= =

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• MEMS actuators move single lens to achieve high precision auto-focusing • Lens is mounted on the actuator, moving the lens along the optical axis achieve autofocusing • Lens position can be determined by measuring the capacitance of the actuator

When no voltage is applied to the actuators. The lens is positioned at “infinity” mechanical stop position

When voltage is applied to the actuators. The lens is moved toward the “macro” position

MEMS AF Design

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MEMS Design Process

MEMS design process optimization has reduced MEMS design cycle

Able to yield functional silicon on the first design/process verification cycle

Improved ability to predict drop performance from FEA modeling New failure modes can still come

up with new designs Continue to improve our design

checklists and our models

Continue to reduce design and validation cycle time

Product quality is built into the new product development process Design validation combined with process validation Advanced custom tools for MEMS design

Design / model

Error budget Monte Carlo

Flow down specifications

Test Build

Assembly

DESIGN VALIDATION

PROCESS VALIDATION

Product specifications

DESIGN VALIDATION

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MEMS AutoFocus Actuator

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MEMS vs. VCM

Voice coil Autofocus MEMS

MEMS is simpler and smaller than today’s Voice coil smartphone Autofocus

8.5 mm x 8.5 mm x 5 mm 12 pieces

6 mm Diameter x 1 mm 3 pieces

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MEMS vs. VCM

MEMS has 1/5th the dynamic tilt of VCM

Peak Dynamic Tilt: 0.052°

• 5x increase in dynamic tilt = up to 2x worse corner image quality

VCM

Peak Dynamic Tilt: 0.262°

MEMS

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MEMS vs. VCM

Heat degrades image quality:

Sensor: Noise DOUBLES every 6° Lens: Corner image quality (MTF) drops 5-10% every 10°

*Controlled measurements taken at 100mm focus with open 1/3” 8MP modules. Larger variance expected enclosed in a phone.

VCM

Time (seconds)

Sens

or t

empe

ratu

re (

°C)

MEMS camera runs 20 C cooler than VCM

MEMS

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MEMS vs. VCM

Focus Dist. Power Consumption (mW)

MEMS A1594 VCM Module 4

10cm 1.0528 123.357

1m 0.9996 55.146

2.5m 1.0024 32.368

Worst case in MEMS modules Best case in VCM modules

MEMS consumes 1/100th the power of VCM Comparison of power consumption with identical hardware (both using

Fujitsu ISP, Sony sensor, and firmware)

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MEMS vs. VCM

MEMS is at least 2 times faster than VCM MEMS AF running on Fujitsu M9M0 ISP

Autofocus Speed (10cm to 1.2m)

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MEMS Actuator Performance • At the threshold voltage, actuator starts to move (17 V in example) • Above the threshold, position is changed by adjusting voltage

• Motion is highly repeatable (multiple curves overlap in example) • Virtually no hysteresis (blue curve is increasing voltage, red is decreasing)

• Actuator is designed to operate up to 33 V but is used up to 31.5 V • Capacitance can be used to determine actuator movement.

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Design Characteristics Stage is robust, repeatable, precise 8F/706 – validated by customer

Capacitance stability 1% (not hermetically

sealed)

Symmetric design keeps lens centered and

fingers centered at all times

High aspect ratio flexures (> 20:1)

Stiffness in travel (z) direction is >1,000 times

softer than in all other (5) degrees of freedom Ensures precise linear motion in z direction

Electrostatic actuation and position sensing

Payload – 4 mg (>100X for other MEMS)

Motion – 100 um (~100X for other MEMS)

Shock – >10000 g shock survivability in a smartphone

BEST COST/PEFORMANCE AF SOLUTION

Thank You