Voxtel SPAD/ SiPM , ROIC, and Multi-channel TDC Technologies

1. Voxtel SPAD/SiPM, ROIC, and Multi-channel TDC Technologies Date: 4/12/2012 Voxtel Contacts: George Williams (georgew@voxtel-inc.com) Vinit Dhulla (vinitd@voxtel-inc.com) Adam Lee (adaml@voxtel-inc.com) Address: 15985 NW Schendel Ave, Suite 200, Beaverton, OR 97006

2. Presentation Agenda • Voxtel Overview • Silicon APD Development • AQC Based ROIC Development • Hybridization Development • Other DOE Related ROIC Development Activity • Multi-channel, Reconfigurable Pulse-processing Instrumentation

3. About Voxtel • Corporate Offices / Voxtel Opto (Beaverton, Oregon) • Contract Administration • Opto Products Group • InGaAs and silicon photodiodes, avalanche photodiodes (APDs), photoreceivers, and focal plane arrays • Readout integrated circuits (ROICs) for imaging, LADAR, and radiation detection • Single-photon-sensitive detectors and instruments • Electro-Optic systems engineering • Voxtel Nano (Eugene, Oregon) • Nano Products Group • Colloidal semiconductor quantum dots (PbS, CdSe, InP, SnTe, etc.) • Rare-earth-doped nanocrystals (ZnS, YVO4, LaF3, etc.) • Ligand design and custom surface functionalization • Optical up- and down-conversion • Security inks and covert taggants • Nanocrystal-sensitized photovoltaic and photoconductive devices • Continuous flow reactors for nanocrystal/quantum dot synthesis • Analytical Facilities

4. Selected Voxtel Products Single-Element InGaAs Photodiodes and APDs InGaAs Photodiode and APD Arrays Free-Space Coupled Photoreceivers Fiber-Pigtailed Photoreceivers CMOS Readout Integrated Circuits Multi-Channel Time Recorder Boards Focal Plane Arrays for Imaging and LADAR

5. Proposed Detector Arrays & ROIC Standards DETECTORS • 50 micron square pixel • 1 x 1mm2 (fiber) and 4 x 4 mm2 (calorimetry)arrays • compatible with face-to-face (f2f) or TSV bonding • Back-illuminated for 300nm response ROICs: • Matched to SPAD arrays • 1 x 1 mm2 • nsec TOF on chip • MHz count rates • 10s photons dynamic range • 4 x 4 mm2 • 100 ps TOF in fabric of SPAD array • 1000s photons dynamic range

6. Back-illuminated Silicon Gm-APD Development • Implemented in a commercial, 200mm CMOS fab • compatible with monolithic circuit integration • compatible with modern 3D wafer stacking technologies (>200mm) • Back-illuminated to improve UV-Blue optical response • Implemented at Tower/Jazz • Domestic source • fine photolithography (0.25µm and 0.18µm) • availability of silicon-on-insulator (SOI) wafer options • shallow Trench Isolation (STI) and Deep Trench Isolation (STI) • double-layer metal-metal (MiM) capacitors • availability of a stitching option for large area, photocomposed wafer-scale integration • mature and stabile • government-funded back-thinning capabiltiy under development • we have transistor radiation models

7. Base Gm-APD Pixel Designs • Implemented on SOI wafers • Heavily doped p+ implant at BOX interface used to biases substrate • STI (shallow trench isolation) / DTI (deep trench isolation) used for (sub)pixel isolation N+/p-well junction N+/”p+ sinker” junction • Sinker is a custom p+ implant developed by Voxtel in the Jazz process • used to achieve full depletion before junction breakdown • used to “focus” high field region and avoid pre-mature edge breakdown N+/p-well junction uses only the standard implants

8. TCAD Models of Gm-APD Pixel Variations Deep Trench Isolation N-well Implanted STI N-well Guard Ring (connected to n+) Multiple Guard Rings

9. Simulated/Measured I-V Curves for Various Doping Levels • Used to calibrate Voxtel’s process models with Jazz fab • process parameters not published by fabs, they need to be deduced • Measured breakdown voltage closely match the simulated values (within 10%) • validates the design and control of the custom sinker implant • Breakdown voltage is uniform between devices on the same wafer and across different wafers.

10. SiPM Performance

11. Measured Gain/DCR vs. State-of-Art (SOA) • Initial DCR is higher then desired • Not enough experimental data to analyze and fully characterize DCR sources • DCR is much better than other CMOS fabricated SiPMs (e.g. RMD) • Recent design run includes experimental DCR test structures and design features • Gain sufficient for photon counting (1 p.e.pulse), photon # discrimination, and integration with electronics

12. Digital SPAD Architecture implemented in CMOS • Demonstrated Digital SPAD features include: • active quenching, • programmable hold-off timing, • threshold detection, • photon counting / time-to-digital converter • in-pixel APD bias NUC, and • integrated fuse • Cross section of Jazz Semiconductors thick film SOI processes. • custom implants used to optimize the process for fabricating low breakdown Gm-APD designs • trench isolation enables isolation of active circuits with the photodetector elements.

13. 35-micron Pitch Digital SPAD Pixel Block Diagram Quench Time: 5.0 – 900 ns Pre-charge Time: 2 – 12 ns Output Pulse Time: 2 – 10 ns • Each pixel features: • an active quenching circuit with globally controlled pre-charge and quench timing • - 3rd generation of an AQC design originally developed for Geiger mode (Gm) • integrated SRAM with “power down” circuits • - enables individual characterization of each pixel in the SPAD array. • - used to disable “noisy” pixels across the array, lowering the detector dark counts

14. 35-micron Pitch Digital SPAD Pixel Layout Monolithically integrated APD AQC and quench delay generator SRAM and power down Output pulse generator and driver • Layout of Digital SPAD pixel design on a 35-µm pixel pitch • An APD was implemented in the monolithic design (upper left hand corner) for test • APD fills 47% of the total pixel area • In hybrid (wafer bonded) designs, the pixel will be shorted

15. VX-808 Digital SPAD Testchip • will be used to evaluate both APD designs • used to re-test s AQC circuits • taped out to Jazz Semi. Jan 2012. (back May 2012) APD and SiPM test structures Pixel array testchip (40 x 40) with 35 µm pixel pitch

16. Wafer-scale Back-thinning Process Starting Wafer Stack Attach Wafer w/3m Bond Remove Handle Wafer Remove BOX Etch to Bond Pads Bond Device

17. Sensor Hybridization (3D Stacking) and Thinning after bonding and thinning, detector mesas are formed (grey areas) and bond pad openings are etched to allow bonding Bonded/Thinned (6” to 8” wafers) Bonded Device 8” ROIC wafer bonded to matching 6” SOI photodiode wafer. Mesa Etch/Pad Opening

18. Reliable Wafer-scale Back-thinning Process Back-thinned SiPM Devices

19. Voxtel SPAD/SiPM Phase II SBIR Efforts Under Review • Topic 61: Wafer-Scale Geiger-mode Silicon Photomultiplier Arrays Fabricated Using Domestic CMOS Fab • Characterize latest generation of Gm APDs fabricated in Phase I • Optimize a low DCR Gm SPAD (SiPM) using Jazz process • Assumes a 25-µm pixel pitch • Optimized for backside illumination • Compatible with large area stitching, but included in program • Topic 63a: Digital Silicon Photomultiplier Array Readout Integrated Circuits • Characterize digital SPAD ROIC fabricated at Jazz in Phase I • Develop a 25 micron pitch ROIC for digital SPADS • Designed for hybrid stacked circuit of bump bond integration • Design includes: • In-pixel AQC • In-pixel (sub)pixel enable • (Optional) monolithic Gm SPAD, which can be shorted for 3D stacked integration* • Sub-block asynchronous TDC • Programmable threshold

20. VX-798: High Dynamic Range, Multi-threshold Photon Counting Sensor VOXTEL PROPRIETARY VX-798 Unit Cell Block Diagram VX-798 Array with Thick, Fully-Depleted Silicon Sensor • Model VX-798 Features • Calibrated, dual-level threshold detection • Programmable 30-bit / (2 x 15-bit) photon counting • Low-noise front end optimized for 10 ns and 150 ns bunch timing • 130 µm pixel pitch, 48 x 48 array, currently developing a full reticle version of design

21. VX-803: Time-Resolved HEP Event Detection with Sparse Readout VOXTEL PROPRIETARY • Model VX-803 Features • Low-noise pixel design with discriminator and time stamp in each pixel – 300 ns timing resolution at 1 ms gate time • Sparse readout of array between bunch train uses pixel “hit” flags for event driven readout • 15 µm pixel pitch, 960 x 448 format array • ROIC designed for wafer –to-wafer hybridization (Ziptronix) • VX-803 (15µm) pixel Layout • Picture of Model VX-803 • VX-803 Noise Contributors • VX-803 Pixel Block Diagram

22. VX-807: Asynchronous, Time-Resolved, Event-driven Photon Detector VOXTEL PROPRIETARY VX-807 Unit Cell Block Diagram • Model VX-807 Features • Low noise amplifier and discrimination designed for soft x-ray (530 eV) single photon detection • Handshaking and address arbitration logic used to handle real-time readout of hit pixels with 40 ns timing resolution • Supports >20 MHz photon count rates • Totally asynchronous operation • 40 um pixel pitch, 492 x 492 full reticle array VX-807 Floorplan VX-807 Simulated Performance

23. VX-803: Rad-hard SOI CMOS Star Tracker SOI CMOS Imager Wafer Photon Transfer Curve • Model VX-803 • Large format, low-noise, mega-pixel, hybrid BSI image sensor • Fabricated on SOI to achieve full depletion using high resistivity silicon • Fabricated on SOI wafers for tolerance to transient singe event effects • Capacitive transimpedance amplifier (CTIA) with correlated double sampling (CDS) • Radiation hard-by-design techniques on a 0.18 µm CMOS process to increase radiation total ionizing does tolerance

24. VX-819: 2D-Array Event-driven Ripple Waveform Sampling VX-819 Pixel Block Diagram VX-819 Pixel Layout • Model VX-819 • Programmable pulse detection circuit • 40 samples in 55 um pixel • Programmable sample rate ( 1 ns minimum) • Used with curve fitting to achieve 50-ps timing resolution VOXTEL PROPRIETARY

25. In Progress: PS-Waveform Recorder (Phase I SBIR Development) Time resolution vs sampling jitter for input signals of 100 photo-electrons. The sampling rate is 40 GSa/s, the analog bandwidth is 1.5 GHz (Ganat 2008) Pulse sampling and timing extraction. (Bogdan, 2009) Time resolution versus analog bandwidth for a fixed sampling rate of 40 GSa/s, for input signals of 20 and 50 photo-electrons (Ganat 2008). The VX-251 shown in the test platform used to assess functionality. Microscope photo of one end of the VX-805 ROIC, showing the landing spot for the APD die.

26. Multi-channel Time-to-Digital Converter (TDC) and Binary Pulse Processor (BPP) • Features for Existing Product • 8 CMOS input channels or 64 LVDS input channels • Timing resolution < 50ps • Measurement range of 13ms (extendable) • Count rates of 20 million counts per second (cps) on each channel • Large internal memory buffer, with a minimum storage capacity of 65,535 events per channel (262,000 events per channel for 8 channel instrument) • Gigabit Ethernet (GbE) to communicate with the host PC. • Single 5V power supply for operation • Software GUI with statistical analysis features • Auto (Cross) Correlation demonstrated with Ƭmin = 3 ns • Binary Pulse Processing, Time-over-threshold, and Multi-threshold Processing • 64, 128, and 512 versions under development

27. High channel Count, Re-configurable Multi-Purpose Pulse-processing Platform • Planned Features • Easily reconfigurable pulse-processing platform with multiple daughter boards to meet different application needs • Application-specific, pluggable front-end modules – time-stamping (analog and digital inputs), analog to digital conversion, auto and cross-correlation • Up to 1000 channels • High timing resolution (tens of pico-seconds to sub-ns, depending on the channel count and application) • Data transfer rates of up to 400 MB/s • Variable measurement times, depending on the application • Ability to time-stamp positive and negative edges • Ability to measure really short pulses (<1ns) • Minimum dead-time between pulses (<3ns) • High input pulse count rates (> 250 MHz) • User friendly software GUI

28. Thank You