Solid-State Photomultiplier for the PRIMEX PbWO4 Calorimeter Erik Johnson1 Christopher Stapels1, Sharmistha Mukhopadhyay1, Paul Linsay1, Rory Miskimen2, Skip Augustine3, and James Christian1 1Radiation Monitoring Devices, Inc., Watertown, MA 2University of Massachusetts, Amherst, MA 3Augustine Engineering, Encinitas, CA Support from DOE

Solid-State Photomultipliers Used for detecting light pulses from scintillation events. Array of photodiodes readout in parallel. Each diode has a binary response to single photons. The response to each diode is associated with a large gain, providing good signal to noise. The number of triggered diodes is proportional to the incident light intensity. Radiation Monitoring Devices, Inc. has built these devices using CMOS technology, which allows integrated circuits on the same silicon die. Explain the distributions. Binary signal from the GPD Charged particles will only trigger 1 pixel, maybe two. DNP: Oct. 26, 2008

Geiger Photodiodes Rq - Vb + Binary signal Optical Photon Rq - Vb p-layer + n-layer SSPMs are built as an array of Geiger Photo-Diodes (GPD). GPD is a reversed biased photodiode operated beyond the diode breakdown voltage. Single pixel DE = Quantum Efficiency•Geiger Probability Geiger Probability is the potential of an electron-hole pair to generate a self-sustained avalanche. Quenching: Passive: ballast resistor, Rq Active: Use transistor to drop the voltage to quench the diode. Binary signal QE corresponds to reflection and absorption GP corresponds to avalanche creation DNP: Oct. 26, 2008

SSPM Design 2 x 2 SSPM array 1.5x1.5mm2 ea. Fill Factor: 61% Gain @ 1 V: 2x106 QEmax: 48% at 520 nm Number of Pixels: 2024 DNP: Oct. 26, 2008

Spectral Response Electronic noise: Small effect (large signal gain) Energy Resolution: Electronic noise: Small effect (large signal gain) Scintillator: Major contribution Detector: Various factors contribute Photon detection (statistical fluctuations) Thermally generated dark noise (dark counts) Excess noise (cross-talk, after pulsing) SSPM Statistics DNP: Oct. 26, 2008

Detection Efficiency Nuclear Instruments and Methods in Physics Research A 376 (1996) 319-334 IEEE Transactions on Nuclear Science, 55, 3 (2008) 1289-1294 Junction is fully depleted, QE ~ independent of excess bias. Electron and hole ionization rates are different. Geiger probability is dependent on whether electron or hole creates the avalanche. DNP: Oct. 26, 2008

Standard Noise Sources Cross Talk Adjacent pixels trigger due to hot-carrier emission. After Pulsing Geiger pulses due to trapped carriers. Dark Counts Thermally excited carriers inducing an avalanche. Magnitude of the noise sources Fluctuations due to these sources effect the noise. Fluctuation is proportional to the magnitude Dark counts are handled with Poisson statistics. Cross talk and after pulsing are handled as excess noise terms. All sources increase with excess bias. DNP: Oct. 26, 2008

Temperature Dependence Dark Counts Thermally excited carriers inducing an avalanche. Cross Talk Adjacent pixels trigger due to hot-carrier emission. After Pulsing Geiger pulses due to trapped carriers Preliminary Decreases Dark counts: thermal excitation is suppressed. Cross talk: hot carrier emission is reduced. (Preliminary) Increase in after pulsing Longer trap life times Mitigated by two effects Fast scintillators (integration times): sample fewer after pulses. Noise is affected by fluctuations in output charge: the charge from after pulses is smallest near the initial pulse in time. DNP: Oct. 26, 2008

Non-Linear Behavior Non-linear response of SSPM. Non-linear transformation between number of triggered pixels and event energy. 22Na LYSO: 1.5 x 1.5 x 3 mm3 Few Pixels Illustration of Saturation Effect Account for non-linear response for accurate energy resolution An “effective integration time” may effectively increase the total number of pixels in the SSPM DNP: Oct. 26, 2008

Pulsed Laser: 635-nm: ~5 ns wide SSPM Statistics Poisson – Good approximation in Linear Response Region The distribution function for the SSPM has a lower and upper bound: Use binomial statistics. Pulsed Laser: 635-nm: ~5 ns wide Excess Noise Cross-talk After Pulsing Binomial SSPM Statistics Poisson Dark Counts Energy resolution affected by SSPM statistics when event triggers > 30% of total pixels DNP: Oct. 26, 2008

Core Design Energy Resolution 2 V Excess Bias Not Optimized T = 0 °C DNP: Oct. 26, 2008

All-Digital SSPM All-Digital SSPM Pixel-level comparator (signal processing) & active quenching qSSPM  Vx(T): (Linear) Fill factor trade-off (reflected light recovery) Provide feedback to make excess bias constant qSSPM is constant 16% Fill Factor 400 pixels per quadrant Testing in progress Feedback Pixel DNP: Oct. 26, 2008

Plans for PRIMEX PbWO4 SSPM PMT Cooled and Dry Vessel Phase-I Task List Determine the detector and readout requirements for the photodetector and ADC. Establish a robust readout protocol for monolithic integration of detector channels. Examine temperature dependences for SSPMs and PMTs. Develop external ADC modules with temperature compensation. Evaluate performance of ADC unit when coupled to PMT and SSPM. Provide a cost analysis of design options. Develop design concepts for SSPM integrated with an ADC. Write Phase I report and Phase II proposal. Key Task Evaluate at RMD using 60Co source. Packaging: light tight and cooled Ship to Jefferson Lab for test beam evaluation. Recently Started Phase-II proposal due mid-March PbWO4 SSPM PMT Cooled and Dry Vessel DNP: Oct. 26, 2008

Cost Analysis Photodetector and power supply Research Prototype Intermediate Production 20 x 20 mm2 pixel 50k pixel device 8.2 x 8.2 mm2 Device Size 2 133 1333 Part or Process per Unit Costs SSPM $5,000 $75 $8 Design and Layout $10,000 $0 CMOS Mask Set Included $675 NRE Packaging PCB $100 $50* $5 - $50 Data Interface $650 (ADI: HSC-ADC-EVALCZ) $6* (USB Interface) $6 ADC $220 (ADI: AD9230-250EBZ) $60* (ADI: AD9230BCPZ-250) $0† - $60 Power Supply Regulator $50 $12* $0† Voltage Supply (AC Adapter) $10 Assembly $800 Total per Device $17,130 $1013 $47 - $152 Costs are in US Dollars and are best estimates * Bulk purchase reduction † Inclusion in the CMOS layout Photodetector and power supply DNP: Oct. 26, 2008

Summary Solid-State Photomultipliers Future Plans Compact High Gain CMOS: Integrated Signal Processing Low Cost Provide PMT-like Energy Resolution Future Plans Evaluation at RMD with test sources Evaluation at JLab Provide a more complete cost analysis (compare PMT to SSPM with integrated signal processing). DNP: Oct. 26, 2008

Application with SSPMs DNP: Oct. 26, 2008

Temperature Dependence Accommodate large temperature range for useful device Geiger Probability Junction Capacitance Excess Bias, Vx Breakdown voltage, VB Proportional to temperature (~50mV per °C) Excess bias inversely proportional. PG is proportional to the excess bias. (~9% per V) Junction Capacitance, CJ (Preliminary) Inversely proportional to temperature (0.5fF per °C) Constant applied bias, temperature decreases: Number of pixels increases Output charge per pixel increases DNP: Oct. 26, 2008

Device Conditions Vx V V CVx RC t t … Used for Signal Integration Quadrant Pixel C (fF) R (kW) Recharge Time (ns) Q1 130 160 21 Q2 270 250 67 Q3 330 290 96 Q4 170 200 34 Vx V V CVx RC t t Pulser Used for Signal Integration 220 pF … Preamp Shaping Amp MCA 10 nF substrate 2kW - Vb + Not Needed DNP: Oct. 26, 2008

Electron/Hole Ionization IEEE Transactions on Nuclear Science, 19, 9 (1972) 1056-1060 DNP: Oct. 26, 2008