Mirasol Displays

MAE 268

Erik Bettis

Josh Saylor

Introduction

• MEMS device developed by Qualcomm– Low power display

• Uses ambient light as source• Operation requires very low voltages

– Replacement for current LCD screens• Cell phones and other small devices

– Enhance viewability in direct light• Brightness of display increases as ambient light

intensifies• Light reflection of up to 50%

Erik Bettis

Current Products

Inventec V112 Smartphone

G-Core Mini Caddy

Hisense C108 Handset

Erik Bettis

Mirasol Technology

• Interferometric Modulation (IMOD)• Low power consumption• Increased readability in direct light• Bistability

– Hysteresis– Built in Memory

• Pixels– Color Generation

• Interference• Spatial Dithering

Erik Bettis

Interfermetric Modulation(IMOD)• Enables reflective, direct view and flat panel

displays• Refresh rates on the order of microseconds

– Video-rate capable• Contrast Ratio: >15:1• Reflectivity: ~ 50%• Wall Street Journal

– Contrast Ratio: 4:1– Reflectivity: ~ 60%

Erik Bettis

Power Metrics

• Mirasol IMOD Display vs. TFT LCD Displays

Video Time Typical Use Multi Media Use

4.5 Hours 206 min 160 min

3.3 Hours 70 min 24 min

Erik Bettis

Increased Readabilty

Erik Bettis

What is Bistability?

• Main feature of Mirasol devices that allows for low power consumption.

• Allows for pixels to be left on or off with near-zero power drain.– Uses imbalance between electro-mechanical

forces and mechanical forces to hold membrane in place with very low power.

• Provides built in memory for pixel placement

Erik Bettis

Hysteresis

• Stage 1– Constant bias voltage holds membrane in open state

• Stage 2– Positive pulse applied to drive membrane into

collapsed state• Stage 3

– Constant bias voltage holds membrane in collapsed state

• State 4– Negative pulse applied to snap membrane back to

open position

Erik Bettis

Bistability and Hysteresis in Mirasol

Erik Bettis

Pixel Design and Color Generation• Pixels create patterns of Red, Green and Blue to create 256k

color range– Interference

• Reflects different wavelengths to create different colors– Red: λ = 675 nm– Green: λ = 520 nm– Blue: λ = 450 nm

– Dithering• Meshes different amounts of Red, Green and Blue to create

new colors– Similar to mixing paint colors on the nano-scale

Josh Saylor

Examples of Spatial DitheringColor perceivedColors as Assigned

Josh Saylor

Interference

Josh Saylor

Side Profile

Thin Film ElectrodeGlass

Spring Analog operating region (225 nm)

Rigid SiO2 Support

Mirror

50 μm

(not to scale)

Pull in distance (450 nm)

Si substrate

Advantage: Analog mirror control allows for multiple colors from a single unit

Blue: 450 nmGreen: 520 nmRed: 675 nm

Proposal of New Design

Josh Saylor

Spring Material

Spring can easily be machined by standard surface micro-machining procedures

SiO2 Support

Compressible Design

0 V

Spring Fabrication

Josh Saylor

Values Used

Max Voltage = 5 V

Permittivity = ε0 = 8.85x10-12 F/m

Area = (50 μm)2 = 2.5x10-9 m2

Initial spacing = 675 nm

k = Fpull-in / Δxspring = 6.1 N/m

Fpull-in = = 1.4x10-6 N

Vpull-in = = 5 V

Mirror will collapse against thin film at

5 Volts

Pull In Voltage and Spacing

Josh Saylor

Current Design42 units per pixelOne color per unit

New Design4 units per pixel

350 μm100 μm

Resolution Scaling Factor of 10

The old 1.4 inch display with 176 x 144 resolution

would increase to 1760 x 1440 pixels with new design

Temporal and Spatial

dithering still possible

Pixel Design of New Layout

Josh Saylor

Questions