How to Specify a SiLM Image Sensor. April 2010

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Archibald Kelley
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1 How to Specify a SiLM Image Sensor April 2010

2 What is SiLM? A layered silicon technology for construction of CMOS imaging sensors providing: Dedicated surface for photodiodes Dedicated surface for pixel circuits Dedicated surface for pixel processing Isolation between PD and CMOS processing Reflector behind photodiodes Expandability to wafer-scale imagers

3 SiLM Structure Reflector Sense Wafer PD Layer TR Layer Mount Wafer

4 The SiLM Photodiode Layer Photodiode (PD) layer Holds only high-performance photodiodes No circuitry in this layer No electrodes or conductors on top - only 200 nm oxide Reflector behind photodiodes Reflector PD Layer

5 The SiLM Transistor Layer Transistor (TR) layer CMOS transistors built with standard 0.18 micron process Entire area available for circuitry Permanently dielectric bond to photodiode layer Connected to photodiodes using standard trench proceses Metal bonded to mount wafer with widely-spaced bumps TR Layer

6 The SiLM Mount Wafer Mount Wafer Provides mechanical support and electrical connections Bonded to circuit layer with low-density bump bonding Adds facility for transistors Supports higher-level control and processing functions Mount Wafer

7 Advantages of SiLM Imagers High photodiode fill factor Nearly 100% High transistor fill factor No shared space with photodiode More space for complex functions Global shutter Noise cancellation Produces a Nyquist sensor without sacrificing function Global shuttering across all platforms very high extinction ratio True bipolar anti-blooming on all cores - No sub-threshold characteristics, good matching Isolated processes Photodiode not subjected to CMOS processes CMOS not subjected/restricted by photodiode processes High-acceptance optical Interface Much thinner dielectric stack ~50 nm vs. 5 µm - Supports high performance AR coating Diode thickness can be tailored for required spectral response High blue response Reflector provides tunable high quantum efficiency Mount wafer can contain Control registers Post processing

8 Scan Control Elements of a SiLM Imager Pixel Control Photodiodes Pixel Core PD Layer TR Layer Mount Layer Pixel Circuits Operation Control Readout Processing Circuitry

9 SiLM Pixel Cores Contain the intrinsic pixel array capabilities Photodiode type and size Pixel processing functionality Availability of pixel options Mate with other sensor elements Mode and configuration functions Scan and readout functions External interfaces Higher-level image processing Provide a starting point for pixel customization Modified spectral response Special in-pixel operations Surface coatings, filters and optical elements

10 Current SiLM Pixel Cores V µm pitch, 100% fill factor photodiode (active mount) Global electronic shuttering for T int > 200 µs V µm pitch, 100% fill factor photodiode (active mount) Global electronic shuttering for T int > 100 µs V µm pitch, 100% fill factor pinned photodiode Global electronic shutter (to 5 ns) 25 ke- full well charge capacity V µm pitch, 100% fill factor pinned photodiode Global electronic shutter (to 5 ns) 100 ke- full well charge capacity

11 Options to Add Functionality Output binning Levels of 2,3,4 or higher in either direction independently Pixel-skip binning for use with filter arrays Sensor controls Dedicated mode control lines Control registers On-chip microcontroller Readout methods Analog, single-ended or differential, one or multiple taps A-to-D methods: converter per column or multiplexed Multiplexed serial digital outputs, one or multiple taps Pixel modifications Filters, coatings or other optical surface structures Extend infrared sensitivity Binning, shuttering, CDS and other in-pixel functions Reflector tailoring Stitching up to wafer-scale

12 Add Functions on the Mount Wafer High-level processing can be accommodated The entire mount wafer surface is available for addition of CMOS circuitry. The sense wafer circuit layer can be changed to accommodate mount wafer functions Mount wafer circuitry can be developed with any pixel core High-level function examples TDI linear Laser ranging (pulse gating) Photon counting Motion compensation Edge finding Data reduction and compression Bayer demosaicing Pixel sequencing Multiple image storage

13 Some Additional Options Packaging Ceramic or hermetic metal Integral coolers Special windows Electron-in detectors Custom pixels for your application Bring us your unique pixel requirements We can put almost any detector that can be made in or on silicon on our sensor layer

14 Bring us your most interesting problems. Let us design a sensor for you.

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