Optical MEMS Technologies for Multi-Spectral Infrared Sensors and Imaging Focal Plane Arrays: from VIS to LWIR

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1 Optical MEMS Technologies for Multi-Spectral Infrared Sensors and Imaging Focal Plane Arrays: from VIS to LWIR Lorenzo Faraone et al. School of EE&C Engineering The Univ of Western Australia

2 ANFF WA Node Facilities Riber 32P MBE HgCdTe semiconductor growth 200 m 2 clean room Full device fabrication technology Wet processing, photolithography, RIE, ICPRIE, PECVD, ICPCVD, E-beam and thermal deposition, RTA, bonding & packaging, 4-wave reactive sputtering Full characterisation facilities spectral responsivity, IV, CV, noise, SEM/TEM/AFM/SLM, magneto-transport up to 16T, DLTS, DCXRD, optical profilometer, IR ellipsometry, etc Extensive system design and modelling Synopsis, Cadence, Sentaurus, Altera & Cyprus Tools, ZEMAX, XFDTD, CoventorWare, ANSYS, ABAQUS, etc

3 ANFF WA Node Areas of Expertise HgCdTe IR detectors (from MBE growth to sensor modules) Micro Electro-Mechanical Systems (MEMS) Semiconductor materials characterisation: e.g. mobility spectrum analysis, scanning laser microscopy, etc GaN and SiC-based High Power/Temperature materials, devices & technology

4 ANFF WA Node HgCdTe MBE Growth In-doped n-type; As and vacancy doped p-type MBE grown CdTe passivation and HgTe/CdTe superlattices Multi-layer devices fabricated on MBE materials

5 8 8 detector array packaged in LCC carrier HgCdTe detector array Fanout Double layer photoresist for In bump fabrication mirror finished IR surface converted n-type p-type HgCdTe CdZnTe sapphire ZnS/CdTe Au/Cr In/Cr Au

6 ANFF WA Node Formal Linkages with Non-University US Govt Labs and Industry (past 10 years) Focused primarily in two areas: mobility spectrum techniques for carrier transport studies, and MEMS-based multi-spectral sensors and imaging FPAs NRL (Washington), Lake Shore, Raytheon, ARL (Adelphi), NVESD (Fort Belvoir), Cree, DARPA, AFRL (WPAFB), DRS, Goodrich ISR, Agilent Technol. Focused primarily on HgCdTe, InAs/GaSb Type II superlattices, SiC, MEMS Linkages have included joint patents, direct research grants, joint research funding, licensing agreements, research contracts, etc Total $$$ in excess of USD$7.5 million (past 10 years)

7 Motivation and overview of why optical MEMS for adaptive infrared sensors and focal plane arrays Operating principles Technologies developed at UWA: Microspectrometer sensors at Infrared wavelengths (SWIR & MWIR) Low temperature MEMS technology compatible with all IR materials Designs for 2-D adaptive focal plane arrays MEMS filters with wide spectral tuning range at low voltages, and with neartheoretical linewidths and extinction ratios

8 image_galleries/ir_zoo/giraffe.html Motivation: IR spectral information: Improved target ID in clutter Lower false alarm rates Chem/bio sensing (food, agriculture, biomedical, defence & security, IEDs

9 Applications in Meat Industry

10 Reconfigurable Multi-Function Sensing WFOV Search & Surveillance Targeting in Clutter Gun Flash Detection Smoke Penetration Navigation NFOV Identification Chemical Detection Adverse Weather Penetration Combat ID and Tagging Many Sensor Functions Can Be Combined into One Adaptive Day/Night EO Sensor

11 Motivation: 200 μm Bench-scale FTIR spectrometer High precision and accuracy over very wide spectral range Expensive Bulky Fragile Microspectrometer Limited spectral resolution and tuning range High speed (extremely low mass) Potentially low cost due to standard IC processing technology Mechanically robust (low mass) Dramatically reduced SWaP

12 The microspectrometer concept Integration of MEMS tuneable Fabry-Perot filter technology with IR sensors and imaging arrays Increased functionality (adaptive) Multi or hyperspectral imaging systems Wavelength agile sensor systems Wider application Wavelength agility opens a wide range of high speed chemical and biological sensor applications, as well as dramatically improved target detection and identification Tuneable, multispectral IRFPAs (Adaptive FPAs)

13 Specifications for field-portable stand-off chem/bio sensing in complex media Not so important: Spectral resolution and tuning range is not critical 20-50nm resolution for NIR/SWIR (uncooled) Max spectral tuning range of one octave matches detector technology: NIR, SWIR, MWIR, LWIR Important: Sensitivity, speed, high optical throughput Compatibility with 2-D multi-spectral imaging arrays Internal wavelength calibration Low cost Essential: Mechanical robustness, reproducibility, stability, reliability Dramatically reduced SWaP 13

14 Specifications for field-portable stand-off chem/bio sensing in complex media 14 A. M. C. Davies, Introduction to near infrared spectroscopy, NIR News, vol. 16, pp. 9 11, Bread dough

15 Transmission How does it work? V Incident IR Reflected IR Mirror Silicon Nitride Cavity Length, d Mirror Detector Spectral filters created by separating mirrors a distance 'd Filter tuned by moving top mirror and changing cavity length d Mirror moved electrically d = 900nm d = 1700nm 100.0% 75.0% Actuators Top mirror 50.0% 25.0% 0.0% Wavelength (nm) Bottom electrode Bottom mirror Top electrode

16 Principle of Operation Transmitted light is detected with a broadband detector Intensity Incident Spectrum Transmitted spectrum Detector output is proportional to the area under this curve Detector Output Wavelength Tuning Voltage V 1 16

17 Principle of Operation Transmitted light is detected with a broadband detector Intensity Incident Spectrum Voltage is increased to change the transmitted wavelength Detector Output Wavelength Tuning Voltage V 2 V 1 17

18 Principle of Operation Transmitted light is detected with a broadband detector Intensity Incident Spectrum Detector Output Wavelength Tuning Voltage V 2 V 1 18

19 Principle of Operation Transmitted light is detected with a broadband detector Intensity Incident Spectrum Detector Output Wavelength Tuning Voltage V 2 V 1 19

20 Principle of Operation Transmitted light is detected with a broadband detector Intensity Incident Spectrum Detector Output Wavelength Tuning Voltage V 2 V 1 20

21 Principle of Operation Transmitted light is detected with a broadband detector Intensity Incident Spectrum Detector Output Wavelength Tuning Voltage V 2 V 1 21

22 Principle of Operation Transmitted light is detected with a broadband detector Intensity Incident Spectrum A range of tuning voltages are used to determine the incident spectrum Detector Output Wavelength V 7 Tuning Voltage V 2 V 1 22

23 IR/MEMS Time Line Early 2004 Late 2004 Early Development of Fabry-Perot MEMs filters HgCdTe infrastructure development of material, detector & packaging technology -photodiodes & photoconductors Detectors with thin film Fabry-Perot Filters R & D partners: (US, EU & Aust.) Defence industry Govt Labs Universities Start-up & IP commercialization: Food & Agriculture Photodiodes with TF-FP Filters Tuneable Photodiodes with TF-FP MEMS Filters Applications & end-users: Food & agriculture Defence & security Tuneable arrays of Photodiodes with Fabry- Perot MEMS Filters New directions: (US, EU & Aust.) LWIR, VIS/NIR Large area PhD s

24 MEMS Integration with IR imaging arrays: Toward Next Generation Intelligent Focal Plane Arrays 24 Adaptive Focal Plane Arrays Integrated, on-pixel reconfigurable, micro-spectrometers Individual pixel-by-pixel wavelength tuning from ROIC IR FPA requirements Low noise High sensitivity Highest performance SWIR, MWIR, LWIR Why MEMS? Increased adaptability of imager/sensor Reduced SWaP Increased portability, robustness, and speed Decreased cost

25 Adaptive Focal Plane Arrays High- Resolution IR FPA Each Pixel tunable State-of-the-Art Hyper-Spectral Imager (HSI) > 50 lbs > 1 ft 3 > $200K MSI/HSI on a Chip Reconfigurable IR FPA Focal Plane Arrays that Think

26 Low Temperature MEMS challenges 26 (DARPA/AFRL/DRS AFPA program) SiN x Membrane HgCdTe Detector 26 Metal Electrode DBR Mirrors Silicon Readout Electronics Key Technology Development Fabrication Temperatures <150 o C Sacrificial Material Low Temperature Scalable Determines cavity length Operating wavelength (SWIR, MWIR, LWIR) Mechanical Thin Film Support Low Temperature Deposition Stress Tuneability Mirrors Conductive Low Optical Loss Low Temperature Deposition Stress Tuneability Metal Layers Stress control

27 Multi-layer dielectric mirrors can exhibit curvature due to stress gradients Compressive Curvature increases linewidth and reduces peak transmission (optical throughput) Tensile Release Sacrificial layer δd = 0 δd = ±15 nm over 100μm δd δd = ±100 nm over 100μm Substrate or detector Curvature needs to be controlled to avoid performance degradation Approx equivalent to 15mm over 100m in a cavity of 1m in length 27

28 Snap-down in parallel-plate tunable optical filters Top mirror Bottom mirror Top electrode V Bottom electrode 33% 67% Parallel-plate electrostatic actuation: snap-down limits spectral tuning range 28

29 Extending the SWIR tuning range: Doubly-supported beam flexures/actuators 29 Measured Data Finite element + optical modeling

30 Measured displacement and SWIR transmittance - Measured displacement Displacement measured using optical profilometer - Fixed-fixed beam analytical model - From transmittance data

31 Hybrid approach: Single-element SWIR microspectrometer Sapphire window Detector Sapphire Window MEMS Filter z y x MEMS Filter Det. TEC InGaAs SWIR Detector on TEC

32 Measured SWIR spectral data demonstrates tuning from 2425 nm to 1620 nm ( ~ 900 nm) 22.4 V (RMS) 0V Demonstrated close to theoretical performance for 3-layer mirrors: 50 nm linewidth with low tuning voltage ( < 25 V) Extinction ratio > 2000 nm Widest reported tuning range for a MEMS-based tunable Fabry-Perot filter

33 Transmission [%] Mid-wave IR hybrid integrated filter/detector: optical performance Initial cavity length of 2.4μm 0.9μm tuning range with voltage tuning Snap down at 1/3 of cavity length (parallel-plate actuation) Voltage range 0-17V FWHM ~200nm (theoretical ~100nm) MWIR Filter V 0V Wavelength [ m]

34 Long-wave IR MSI/HSI: Key to Detecting Targets in Deep Hide The sum of a hundred narrow band images in the band of 8-12 m The difference of two narrow bands, one at ~9.7 m and one at ~8.3 m Although two bands work, the bands vary with time and environment: Require adaptive IRFPAs We want to avoid generating the so-called Hyperspectral Cube How to do on-the-fly spectral and spatial processing??

35 Transmission (%) Modelling of Long-Wave IR Fabry-Perot Transmission for LWIR Multi-Spectral Adaptive Imaging forp forerot 100 Transmission d=4 m d=4.7 m d=5.4 m d=6 m Wavelength ( m)

36 Large area Fabry-Perot filter for 2-D adaptive IR focal plane arrays

37 Recent progress for chem/bio stand-off sensors New mirror design: Predicted performance (SWIR)

38 Recent progress for chem/bio stand-off sensors New mirror design: Predicted performance (VIS/NIR)

39 ANFF WA Node capabilities in optical MEMS for multi-spectral IR sensors & arrays Tuneable IR sensors based on MEMS in the SWIR ( µm) and MWIR (3-5 µm) using the same materials/mirror technology Low-temperature MEMS fabrication compatible with all IR detector materials: makes possible hybrid or monolithic integration in 2-D adaptive focal plane imaging arrays ANFF WA Node capabilities in optical MEMS for multi-spectral IR sensors & arrays Near-theoretical performance in SWIR: wide tuning range of 900nm using < 25 V, linewidth ~50 nm (3-layer mirrors), extinction ratio > 120, switching speed < 50 microsec) Currently finalising IC chip design for internal wavelength calibration, and developing prototype portable SWIR microspectrometer instrument and commercialisation plan for chemometric sensing in food & agriculture Currently investigating materials & technologies for extension into VIS/NIR and LWIR wavelength ranges, and developing very large-area (multi-mm x multi-mm) tuneable filter technologies for large format 2-D focal plane adaptive imaging arrays