Wright State University

Transcription

1 Wright Stte University EE480/680 Micro-Electro-Mechnicl Systems (MEMS) Summer 2006 LVern Strmn, Ph.D. Assistnt Professor Dept. of Electricl nd Computer Engineering Emil: Opticl MEMS 1 2 Opticl MEMS: MOEMS Micro-Opto-Electro-Mechnicl Systems (MOEMS) Opticl MEMS Electromgnetic Spectrum Energy of quntum of electromgnetic rdition: E = hf = hc/λ Opticl Electricl 380 nm (0.38 µm) Visible 720 nm (0.72 µm) MOEMS MEMS γ-rys X-rys Frequency (Hz) Ultrviolet Infrred mm wve (EHz) (PHz) (THz) (GHz) UHF VHF (MHz) 10 6 ULF (khz) 10 3 Additive Color Mixing Mechnicl Wvelength (m) (Å) (nm) 10-6 (µm) (mm) (m) (km) (Mm) 4 1

2 Mirrors & Mirror Arrys Bem Steering Simple Reflection Corner Cube Reflector Grting Phsed Arry Lenses Refrctive Diffrctive Systems Overview Mirrors Different mterils reflect different wvelengths with vrying efficiency -- lmost nything cn be form of mirror. Reflectivity: the percentge light reflected from surfce t given wvelength ex. elementl comprison t 1 µm wvelength Web Elements 5 6 Mirrors: Reflectnce Mirrors: UV Reflectnce W. Driscoll nd W. Vughn, Hndbook of Optics, McGrw-Hill, W. Driscoll nd W. Vughn, Hndbook of Optics, McGrw-Hill, UV Visible Spectrum IR UV 7 8 2

3 Mirrors: IR Reflectnce Si Mirrors: Distortion IR 10 mm thick Si smple W. Driscoll nd W. Vughn, Hndbook of Optics, McGrw-Hill, Most mirrors re fbricted from surfce micromchining Some drwbcks cusing distortion in reflected imge include: Deposited lyers conform to the topology of lower lyers, therefore, embossing the mirror surfce. Residul stress in deposited lyers or combintions of lyers cn deform the mirror surfce Solutions include: Thinner reflective cotings Stiffer mirror structures Avoid topology under mirror by design Use bcksides of lyers through ssembly Use fbriction processes with plnrized lyers More pproprite combintions of multi-lyer mterils Different fbriction processing conditions 9 10 Mirrors: : Fbriction Mirrors: : Fbriction CRONOS -- The Multi-User MEMS Processes, or MUMPs, 1992, 15 copies of 1 cm 1 cm die, $3, μm 0.75 μm oxide2 2 μm poly1 2 μm 0.5 μm 0.6 μm oxide1 poly0 nchor1 vi poly2 0.5 μm metl Phosphosilicte Glss highly doped with P region nchor μm Cr (100) silicon wfer, n-type (P), 1-2 ohm-cm resistivity 100 mm dimeter, μm thickness Metl (gold) Polycrystlline Silicon (doped with P) Oxide (PSG: Si0 2 doped with P) Nitride (Si 3 N 4 ) Crystlline Silicon 0.75 μm dimple nchor1 & vi 11 SUMMiT IV & V, Sndi Ntionl Lbortory Polycrystlline Silicon 100 copies of 6.34 mm Oxide (Si0 2 deposited from TEOS tetr-ethyl-ortho-silicte) 2.82 mm die, $10,000 Nitride (Si 3 N 4 ) V provides 5th plnrized lyer of poly Crystlline Silicon Mx etch hole spcing 38 μm Mx dimple spcing 75 μm 2.25 μm 5.6 μm CMP to μm 1.5 μm 1 μm 2 μm 0.3 μm 0.8 μm 0.63 μm mmpoly3 scox3 mmpoly2 mmpoly1 scox1 scox1 cut mmpoly0 silicon nitride silicon dioxide 0.5 μm dimple μm scox2 scox3 cut mmpoly1_cut scox2 Globl oxide 2 correction for MUMPs-like lyout mmpoly1cut scox1 cut <100> silicon wfer, n-type, 2-20 ohm-cm resistivity, 6 dimeter, 675 μm thickness scox3 cut dimple μm nitride cut Avilble CAD Lyers & Minimum Width (μm): mmpoly3_cut 1 mmpoly3 1 scox3_cut 2 dimple3_cut 1.5 mmpoly2_cut 1 mmpoly2 1 scox2_cut 2 scox2 1 mmpoly1_cut 1 mmpoly1 1 pin_joint_cut 3 scox1_cut 2 dimple1_cut 1 mmpoly0 1 nitride_cut 1, mx 4 3 μm pin joint cut 12 3

4 Mirrors: : Residul Stress MUMPs exmples: 150 nm thick gold Poly2 Simple Reflection Gold Poly2 Ox2 Poly1 Cown, 1998 Reid, 1997 Gold Poly2 Poly1 Cown, µm Gold on Poly2 D. Burns, Microelectromechnicl Opticl Bem Steering Systems, AFIT Disserttion, Gold Poly Corner Cube Reflector Modultion device -- signl lwys returns to source if mirrors re orthogonl to ech other. Mirrors: Bem Steering Diffrction Grtings Sctter reflected in discrete directions: nλ sin( θ n) = where n is the discrete order, θ n is the order direction, λ is the wve length, nd is the period of the grting elements. Reflected Light Incident Light 0 th 1 st Grting interference orders result when light, reflected off of grting elements, combines constructively in the fr field. Reid, 1997 θ n n th order

5 Grting Light Vlve (GLV) by Silicon Light Mchines Destructive interference ttenutes 0 th order. Grting Light Vlve (GLV) by Silicon Light Mchines (n=1) λ/2 d=λ/4 The mximum diffrcted intensity of the first order is when d = λ/4. A pixel nλ sin( θ n) = For sme θ, but different colors, choose different such tht λ/ is sme. -or- Build one pixel for red nd deflect the sme pixel less for green nd blue Grtings cn be ngled to direct the 0 th order intensity into the direction of higher order, therefore, enhncing the higher order direction. Incident Light nλ sin( θ n) = γ n = θ n /2 Reflected Light n th order θ n γ n D. Burns, Microelectromechnicl Opticl Bem Steering Systems, AFIT Disserttion,

6 n = 0 Phsed Arry A digitl pproximtion of bem steering with single tilted mirror. n = 1 n = 2 n = 3 D. Burns, Microelectromechnicl Opticl Bem Steering Systems, AFIT Disserttion, n = 4 21 D. Burns, Microelectromechnicl Opticl Bem Steering Systems, AFIT Disserttion, Overview Lenses: Refrctive Mirrors & Mirror Arrys Bem Steering Simple Reflection Corner Cube Reflector Diffrctive Grtings Phsed Arry Lenses Refrctive Diffrctive Systems

7 Lenses: Refrctive Reflowed BCB lens for VCSEL de-centered lens bem steering Lenses: Refrctive UV curble polymer lenses for 2-D scnning A. Tuntrnont et l., "MEMS-Controllble Microlens Arry for Bem Steering nd Precision Alignment in Opticl Interconnect System," Proceedings of the 2000 Solid-Stte Sensor nd Actutor Workshop, pp , June 4-8, S. Kwon et l., Stcked Two Dimensionl Micro-Lens Scnner for Micro Confocl Imging Arry, Lenses: Refrctive Lenslet rrys with piston micromirrors for berrtion correction using phse ltertion. Lenslet Arry,Nippon Sheet Glss Compny, 250 µm dimeter. 540 µm Thick Glss Spcer UV curble epoxy Micromirrors Lenses: Diffrctive Fresnel Lens Diffrction nd constructive interference shpe the nerfield light bem exiting the lens. 2 Rm f = mλ where f is the focl length, R m is the rdius of the outer zone, m is the lrgest integer number of zones in the lens, nd λ is the wvelength of the source. m = 1 m = 2 m = 3 J. Bouchrd, MS Thesis, AFIT, 1997 A. Tuntrnont et l., "Pckging of Lenslet Arry on Micromirrors," Proceedings of the SPIE `99, vol. 3631, pp , R pin PGA

8 Mirrors & Mirror Arrys Bem Steering Simple Reflection Corner Cube Reflector Grting Phsed Arry Lenses Refrctive Diffrctive Systems Overview Opticl Systems Surfce micromchined VCSEL scnning system J. Bouchrd, MS Thesis, AFIT, Opticl Systems Opticl Systems Texs Instruments Digitl Micromirror Device TM 16 µm 3-Chip, Texs Instruments Digitl Micromirror Device TM