23 Nov 09

Pixilated Photon Detectors and possible uses at ILC and SLHC

WSU, 23 Oct 09 Rubinov “at” fnal.gov Rubinov, WSU HEP seminar 1

-- T. Nakaya (Kyoto) @ Pixel08 --

Intro to SiPM

 Q: What is an SiPM?

 A:

SiPM (Silicon Photo Multiplier) MRS-APD (Metal Resistive Semiconductor APD) SPM (Silicon Photo Multiplier) MPGM APD (Multi Pixel Geiger-mode APD) AMPD (Avalanche Micro-pixel Photo Diode) SSPM (Solid State Photo Multiplier) GM-APD (Geiger Mode APD) SPAD (Singe Photon Avalanche Diode) MPPC (Multi Pixel Photon Counter)

P

ixelated

P

hoton

D

etector

From Yamamoto

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Photodiodes, Avalanche, Geiger Mode

From A Para (Fermilab) Photodiodes: • • p-n junction , reverse bias Electron-hole pair generated by an incoming • • • • photon drifts to the edges of the depleted region I(t) = QE * q * dN/dt(t) Absolute calibration No gain Suitable for large signals

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Photodiodes, Avalanche, Geiger Mode

From A Para (Fermilab) • Avalanche Photodiodes: • • Photodiodes operating at higher bias voltage Higher voltage carriers   stronger electric field impact ionization  Gain  higher energy of drifting (Im)Balance between the number of carriers leaving the depletion region and the number generated carriers per unit time: dN leave /dt > dN generated /dt • Stochastic process: signal quenches when the ‘last’ electron/hole • fails to ionize.

Large fluctuations of the multiplication process  Excess noise factor (beyond-Poisson fluctuations) Gain fluctuations

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Photodiodes, Avalanche, Geiger

From A Para (Fermilab)

Mode

• Geiger Mode Avalanche Photodiodes: Avalanche Photodiodes operated at the elevated bias voltage. • Larger field faster   carriers gain kinetic energy shorter mean free path • • Breakdown voltage: nothing really breaks down, but dN leave /dt = dN generated /dt (on average) at this voltage Some electrons can generate self sustaining avalanche (current limited • eventually by the series resistance) Probability of the avalanche generation • increases with bias voltage (electric field) Operation mode: one photon  (sometimes) ~1e6 electron avalanche

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First prototype of MAPD

(MRS APD 1989)

First metall-resistor-semiconductor A.Gasanov, V.Golovin, Z.Sadygov

APD (MRS APD) structure was designed (russian patent #1702881, from 10/11/1989) by PDE of MRS APD is just few %

23 Nov 09 Rubinov, WSU HEP seminar

Low-light intensity spectrum of MRS APD (A. Akindinov et. al, NIM387 (1997) 231

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Q=C D *(V bias V bd )

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Intro to SiPMs

 Analogy  When comparing PMTs to SiPMs, SiPMs enthusiast usually list advantages of SiPMs BORING and PREDICTABLE  I list advantages of conventional PMTs on next slide from a tube company

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PMT vs SiPM

Adapted from IEEE & Eric Barbour Tubes: Advantages 1. Characteristics highly independent of temperature.

2. Wider dynamic range, due to higher operating voltages.

3. Very low dark current.

SiPM: Disadvantages 1. Device parameters vary considerably with temperature, complicating biasing. 2. May need cooling, because lower operating temperature may be required.

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Analogy?

I think we have seen transition from vacuum tubes to solid state before. Transistors are not tiny vacuum tubes and SiPMs are not tiny PMTs I think that the reason we have transistors instead of tubes boils down to this: $

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Is the SiPM the perfect LLL sensor?

• Die eierlegende Woll-Milch-Sau (german) (approximate english translation: all-in-one device suitable for every purpose) R. Mirzoyan

23 Nov 09

There will be different devices optimized for different applications

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SiPM Animal

 Research in SiPMs is very active, in many different directions – I’m not going to do a survey  Extended blue sensitivity (Cherenkov light, dual readout calorimetry)  Increased PDE ( muon detectors)   Reduced crosstalk (improved noise factor) Improved timing (PET)   Large area (Cherenkov) Increased dynamic range (Calorimeters) 

23 Nov 09

LOWER COST (everyone)

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Areas of interest for LHC

 Issues of special interest to SLHC (more detail on CMS specifics later)  Radiation hardness  Dynamic range/Linearity  Stability (radiation, temperature and time)  CERN has a strong, active community working on all these issues

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Areas of interest for LC

 Issues of special interest to LC (more detail on SiD specifics later)  Blue sensitivity  Cost/unit area  Optical coupling to detector  Calice is a strong collaboration doing fantastic work on these areas

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Understanding SiPM operation

 Here I'm going to focus on 2 issues  DC measurements  Vb determination  Rquench determination  Cross talk measurement  Pulse measurements  Afterpulsing measurements

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DC Measurements

   Static characteristics - IV curves at fixed temperatures:   Keithley 2400 sourcemeter Temperature controlled chamber  Labview data acquisition program Forward bias  series (quenching) resistance Reverse bias  breakdown voltage, integral behaviour of the detector s a function of the operating temperature

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Forward Bias Scan

Limited by quenching resistor dI/dV = 1/R Exponential growth with V Resistance decreases with temperature (polysilicone)

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Detector type 25  50  100 

Quenching Resistance Summary for MPPCs

1/R dR/dT Quenching Resistor @ 25 o C, k  200 105 85 dR/dT k  / o C 2.23

1.08

0.91

0.011

0.010

0.011

From A Para (Fermilab)

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100 pA From A Para (Fermilab)

23 Nov 09

Reverse Bias Scan

Quenching resistance Temperature ‘ 1 V above breakdown I~5x10 -7 A Gain ~ 4x10 6 Photodiode’ current level ~ 10 -13 A How relevant is the current below the breakdown voltage?

Breakdown

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Vbd(T). Preliminary analysis

23 Nov 09

August 29 th 2008 Diego Cauz University & INFN of Udine 30 29 28 33 y = 0.0002x

2 + 0.0482x + 29.168

32 31 27 -50 -40 -30 -20 -10 0

T (C) Rubinov, WSU HEP seminar

10 20 30 40

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Cross Talk Measurement

23 Nov 09

Single avalanche rate Single + 1 cross talk Single +2 cross talk Single +3 cross talk Ratios of rates give relative probabilities of 1,2,3 extra pixels firing due to cross-talk

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Cross Talk Rates as a Function of Bias Voltage 23 Nov 09

• Cross talk probability increases with the bias voltage • Cross talk probability is bigger for larger size pixels But… The cross talk is mediated by infrared photons produced in the avalanche, hence is ought to be proportional to the gain. And different size pixel detectors have different gain !

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Cross Talk Probability as a Function of Gain

• • At the same gain the cross-talk probability is much larger for smaller size pixels At the operating point the Hamamatsu detectors have very small cross talk (~few %)

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Pulse measurements

23 Nov 09

   MPPC-11-050C#37 at 71.1deg F operating at 69.81 (recommended V is 70.02 at 25C) Current reading is 0.044uA

1pe is about 13.25mV

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23 Nov 09

A little bit about after pulses

• • Observed signal grows with the bias voltage. This growth has several components: increase of the gain increase of afterpulsing.

The latter is a much bigger effect. So what?? Afterpulses provide a kind of additional gain. True, but this contribution fluctuates (excess noise factor).

 degrades the charge measurement resolution Relative width of the observed pulse height spectrum slightly decreases with bias voltage for 10 nsec gate (presumably a reflection of the increased number of detected photons), but it increases for longer gates.

Bottom plot shows a contribution to resolution from fluctuations of the afterpulses contribution in different gates.

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23 Nov 09 Detector Recovery / Afterpulsing

   Pulse arrival distribution: clear afterpulsing for about~ 1  sec At least two components:  1 =39 nsec  2 =202 nsec These components probably correspond to traps with different lifetimes

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F. Retiere @ NDIP08 S10262-11-050C 

short ~15ns



long ~85ns Time after the first pulse (ns) 23 Nov 09 Dark-noise rate Time after the first pulse (ns ) Rubinov, WSU HEP seminar 29

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 After subtracting the effects of cross-talk + after pulse, the dark noise is found to be linear to  V.

23 Nov 09 Rubinov, WSU HEP seminar

F. Retiere @ NDIP08

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SiPM pulse shape

 Actually, there is some subtle issues in measuring pulse shape

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   The idea is to model the avalanche as a fast, brief (almost) short across a capacitor (Cdet) which is then recharged through a resistor (Rq)  this is one micro pixel, so 1 pe by definition Also include parasitic capacitance across this resistor (Crq) Also model the rest of the device by a collection of Cdetp, Rqp, Crqp  the parallel stuff is important, it gives that characteristic “kink”

This kink is this plus this There are 4 values of Crq from 1 to 10 fF. So Crq is important for “spike” but not “tail”

Crq= 10fF, 5fF, 2.5fF, 1fF   and this is what we are left with...

So the size of the “spike” makes a huge difference to the shape of what is observed- including the integral

  But, the slow component is not so affected This fig has 8 plots: before and after the filter for each value of Crq

   But its even worse than that...

The details of the assumed filter make a big difference as well I picked this very gentle, 6db stop band filter to prevent this...

For this run, I dropped the Crq=10fF curve These are 5fF, 2.5fF and 1fF curves recall that Cdet is 3fF for this MPPC 025u   ... how about we lower the HiFreq cutoff and concentrate on the shape of the falling edge. Lets say cut at 100MegHz So that corresponds to digitizing at 200MSPS

Simulation vs reality

40mV 30mV 20mV 10mV 70mV 60mV 50mV 0V -10mV 0.98us

1.00us

V(BPASS1:out) 1.02us

1.04us

1.06us

1.08us

1.10us

1.12us

1.14us

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1.16us

1.18us

Using SiPMs

23 Nov 09 Until you have spread your wings, you will have no idea how far you can walk despair.com

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CMS

 Two approaches  Straight replacement of the HPD  Coupling individual fibers to individual SiPMs: Electrical Decoder Unit

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CMS

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Linearity



number of cells is the issue 23 Nov 09 Rubinov, WSU HEP seminar 43

23 Nov 09

Radiation is an issue

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EDU

 The EDU  100% compatible with existing mechanics/optics

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CMS

Either of these could use fantastic new devices from Zecotek

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MAPDs main characteristics

MAPD-1 with surface pixels ( p-type substrate ) 556 pixels*mm -2 MAPD-3N with deep microwells ( n-type substrate ) 15 000 pixels*mm -2

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ILC- SiD

 For SiD there are two possible uses of SiPM  HCAL : 3x3 cm cells directly coupled to SiPMs  Tail catcher/Muon system with scintilator strips and WLS fibers coupled to SiPMs

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Scint HCAL for SiD

The key issue here is coupling of the scintillator to SiPM Northern Illinois University has some very clever and pioneering work on this (basic idea is to put a dimple in the center of the cell) We have made an Integrated Readout Layer board for tests of these cells

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SiD muon system

 For SiD muon system there are 3 main issues 1. Cost 2. Cost 3. Cost

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Our setup

Detail of optical coupling and adopter board using Keithley 2400 for bias (not shown)

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MTest 2008

Beam from Nov10 to 16 Minerva test of TOF counters Added one bar with SiPM for testing (Ham, IRST) Using NIM based 6ch amp built at Fermilab for this work Using optical coupling designed at Notre Dame Using 120 GeV proton beam (1in x 1in spot) Very preliminary results below

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Single PE signals

 Scope traces 5mv/div using LED

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Ham-100 during beam spill

Notice the Y scale is 100mv/div!

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IRST SiPM with 1.8m sint in 120Gev Beam at 34V, I=1.1uA

Notice the Y scale is 100mv/div!

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Summary of test beam

 If you have enough photons, SiPMs will make PERFECT muon detectors.

 So the questions are:  Size of scintillation strip and WLS fiber diameter (cost)    Length of strip and WLS fiber (cost) Area of the SiPM (coupling the fiber to the SiPM) (cost) Electronics to readout the SiPM – does not drive the cost

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Conclusion

We are on a cusp of a revolution in Low Light Level photo detectors.

The only questions is are we going to be manning the barricades

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The Future

 I have seen the future of SiPM readout  Readout electronics will be integrated into the SiPM!

  because  SiPM is an inherently digital device We ALWAYS convert the signal from the SiPM to digital So why do we have an analog step in between?!?

2pe 1pe 0pe ADC 2pe 1pe 0pe

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The Future

 Ingredients required for integrated readout 1. SiPM is CMOS compatible RMD makes SiPMs through Mosis 2. Will work for in HEP applications Pixel architectures have demonstrated readout of arrays like this 3. Cost effective (in volume)

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So why DIGITAL-ANALOG-DIGITAL?

 Because this requires an ASIC  The people who make SiPMs do not know what we want  The people who know what we want do not make SiPMs (yet) Application Specific IC has to have a specific application

Because it gives us the most flexibility

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Back from the future

 Our current strategy is to maximize flexibility  which is the opposite of what we eventually want

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Next step(s): 4ch board

    Still very generic, but now think infrastructure Best available commercial components without heroic efforts (~1ns resolution, ~400 pe range)  Integrated with SiPM specific features (bias generator, current readback, temp sensor) Optimized for medium ch count (dozen(s) SiPMs) Flexible: using 50ohm input, generic daughter board connection to support faster readout/more memory  Large FPGA to allow DSP and TDC features

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Next step(s)

 Still very generic, but now think infrastructure

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 Still very generic, but now think infrastructure CW bias generator 2 stages of diff amps 250MSP S ADCs bias offset/ch daughter brd for faster interface simple USB interface hi res current readback/ch largish FPGA

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 Still very generic, but now think infrastructure CW bias generator bias offset/ch hi res current readback/ch

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Near future

 Move from more generic to more specific  Develop a simple ASIC  Optimize for 100s of SiPMs

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