A photoncounting detector for exoplanet missions Don Figer

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A photon-counting detector for exoplanet missions Don Figer 1, Joong Lee 1, Brandon Hanold

A photon-counting detector for exoplanet missions Don Figer 1, Joong Lee 1, Brandon Hanold 1, Brian Aull 2, Jim Gregory 2, Dan Schuette 2 1 Center 2 MIT for Detectors, Rochester Institute of Technology Lincoln Laboratory Cf. D

Detector Properties and SNR Cf. D 2

Detector Properties and SNR Cf. D 2

Exoplanet Imaging Example • The exposure time required to achieve SNR=1 is much lower

Exoplanet Imaging Example • The exposure time required to achieve SNR=1 is much lower for a zero read noise detector. Cf. D 3

Photon-Counting Detectors • Photon-counting detectors detect individual photons. • They typically use an amplification

Photon-Counting Detectors • Photon-counting detectors detect individual photons. • They typically use an amplification process to produce a large pulse for each absorbed photon. • These types of detectors are useful in low-light and high dynamic range applications – – – Cf. D nighttime surveillance daytime imaging faint object astrophysics high time resolution biophotonics real-time hyperspectral monitoring of urban/battlefield environments orbital debris identification and tracking 4

Operation of Avalanche Photodiode Linear on Geiger mode on Linear Geiger quench mode avalanche

Operation of Avalanche Photodiode Linear on Geiger mode on Linear Geiger quench mode avalanche Current off arm Vdc + DV Vbr Cf. D Voltage 5

Performance Parameters Single photon input ü Photon detection efficiency (PDE) Ø The probability that

Performance Parameters Single photon input ü Photon detection efficiency (PDE) Ø The probability that a single incident photon initiates a current pulse that registers in a digital counter APD output Discriminator level ü Dark count rate (DCR) Digital comparator output Ø The probability that a count is triggered by dark current Cf. D time Successful single photon detection 6 Photon absorbed but insufficient gain – missed count Dark count – from dark current

Avalanche Diode Architecture Cf. D 7

Avalanche Diode Architecture Cf. D 7

Zero Read Noise Detector ROIC Cf. D 8 8

Zero Read Noise Detector ROIC Cf. D 8 8

Zero Noise Detector Project Goals • Operational – Photon-counting – Wide dynamic range: flux

Zero Noise Detector Project Goals • Operational – Photon-counting – Wide dynamic range: flux limit to >108 photons/pixel/s – Time delay and integrate • Technical – Backside illumination for high fill factor – Moderate-sized pixels (25 mm) – Megapixel array Cf. D 9

Zero Noise Detector Specifications Optical (Silicon) Detector Performance Phase 1 Goal Parameter Format Phase

Zero Noise Detector Specifications Optical (Silicon) Detector Performance Phase 1 Goal Parameter Format Phase 2 Goal 256 x 256 1024 x 1024 25 µm 20 µm zero Dark Current (@140 K) <10 -3 e-/s/pixel QEa Silicon (350 nm, 650 nm, 1000 nm) 30%, 50%, 25% 55%, 70%, 35% 90 K – 293 K 100% Pixel Size Read Noise Operating Temperature Fill Factor a. Product of internal QE and probability of initiating an event. Assumes antireflection coating match for wavelength region. Cf. D 10

Zero Noise Detector Specifications Infrared (In. Ga. As) Detector Performance Phase 1 Goal Parameter

Zero Noise Detector Specifications Infrared (In. Ga. As) Detector Performance Phase 1 Goal Parameter Format Phase 2 Goal Single pixel 1024 x 1024 25 µm 20 µm Read Noise zero Dark Current (@140 K) TBD <10 -3 e-/s/pixel QEa (1500 nm) 50% 60% 90 K – 293 K NA 100% w/o mlens Pixel Size Operating Temperature Fill Factor a. Product of internal QE and probability of initiating an event. Assumes antireflection coating match for wavelength region. Cf. D 11

Zero Noise Detector Project Status • A 256 x 25 mm diode array has

Zero Noise Detector Project Status • A 256 x 25 mm diode array has been bonded to a ROIC. • An In. Ga. As array has been hybridized and tested. • Testing is underway. • Depending on results, megapixel silicon or In. Ga. As arrays will be developed. Cf. D 12

Air Force Target Image Cf. D 13

Air Force Target Image Cf. D 13

Anode Current vs. Vbias and T Cf. D 14

Anode Current vs. Vbias and T Cf. D 14

Dark Current Cf. D 15

Dark Current Cf. D 15

GM APD High/Low Fill Factor Cf. D 16

GM APD High/Low Fill Factor Cf. D 16

GM APD Self-Retriggering Simulated Histogram of Avalanche Arrival Times Cf. D 17

GM APD Self-Retriggering Simulated Histogram of Avalanche Arrival Times Cf. D 17

Radiation Testing Program Overview

Radiation Testing Program Overview

Building Radiation Testing Program • Simulate on-orbit radiation environment – choose relevant mission parameters:

Building Radiation Testing Program • Simulate on-orbit radiation environment – choose relevant mission parameters: launch date, mission length, orbit type, etc – Determine radiation spectrum (SPENVIS) • Transport radiation particles through shielding to estimate the radiation dose on the detector (GEANT 4) • Choose beam properties • Design/fab hardware • Obtain baseline data (pre-rad) • Expose to radiation • Obtain data (post-rad) Cf. D 19

Mission Parameters • 2015 launch date, 5 and 11 year mission durations • Radiation

Mission Parameters • 2015 launch date, 5 and 11 year mission durations • Radiation flux depends on relative phasing with respect to solar cycle • Choose representative mission parameters specific to each type of orbit – – L 2 Earth Trailing Heliocentric Distant Retrograde Orbits (DRO) Low Earth Orbit (LEO) – 600 km altitude (TESS) • Solar protons – ESP model – Geomagnetic shielding turned on • Trapped e- and p+ – – Cf. D Inside radiation belt AP-8 Min (proton) model AE-8 Max (electron) model Over-predicts flux at high confidence level setting (from SPENVIS HELP page) 20

Orbits Sun-Earth Rotating Frame DRO Earth Trailing Earth DRO 700, 000 ± ~50, 000

Orbits Sun-Earth Rotating Frame DRO Earth Trailing Earth DRO 700, 000 ± ~50, 000 km radius from Earth Propagated ~10 years SIRTF Earth Launch C 3 ~ 0. 05 km 2/s 2 185 km altitude 28. 5° inclination DRO Insertion ~196 Days + L Delta-V ~150 m/s Sun L 2 Earth WMAP Cf. D 21 GIMLI Top View (North Ecliptic View)

Integrated Particle Fluence DRO L 2 LEO Earth Trailing Cf. D 22

Integrated Particle Fluence DRO L 2 LEO Earth Trailing Cf. D 22

Total Ionizing Dose and Non-Ionizing Dose (at L 2) Cf. D 23

Total Ionizing Dose and Non-Ionizing Dose (at L 2) Cf. D 23

Radiation Testing Program • Now that we know the radiation dose the detector is

Radiation Testing Program • Now that we know the radiation dose the detector is likely to see, we need to build a radiation testing program that is going to simulate the radiation exposure on orbit • We need to choose right beam parameters • Energy, dose rate, particle species • Then, choose radiation facility based on factors above as well as our hardware setup requirements • Vacuum, cryogenics, electrical • We make measurements of relevant quantities pre-, during, post-irradiation to characterize change in detector performance Cf. D 24

Beam Parameters • We want to expose the device to 50 krad (Si). •

Beam Parameters • We want to expose the device to 50 krad (Si). • Due to practical considerations, we can only irradiate the device with a mono-energetic beam. • A device subjected to 50 krad would see 1. 18 e 9 Me. V/g of displacement damage dose (DDD) on orbit at L 2. • Ideally, a 50 krad exposure to the proton beam should also yield a DDD of 1. 18 e 9 Me. V/g to simulate condition on orbit. • For 60 Me. V proton beam, the corresponding DDD to a 50 krad exposure is 1. 26 e 9 Me. V/g. Cf. D 25

Beam Parameters • 60 Me. V happens to be where the proportionality between TID

Beam Parameters • 60 Me. V happens to be where the proportionality between TID and DDD on-orbit is preserved – This depends on thickness of shielding. But if we choose energy around 60 Me. V, the proportionality should be more or less preserved. • Dose Rate – MIL Std 883 Test Method 1019 recommends 50 to 300 rad/sec, although this is for gamma ray beam – 50 rad/sec will still allow us to complete a radiation exposure run in reasonable amount time (~17 min. ) – It makes sense to follow this as higher the rate more chance the device breaks and for dosimetry reasons Cf. D 26

Estimate of Induced Dark Current • KDE = JD/ED =q/(A* )*Kdark= 2. 09 n.

Estimate of Induced Dark Current • KDE = JD/ED =q/(A* )*Kdark= 2. 09 n. A/cm 2/Me. V at 300 K – This gives conversion formula to convert ED to density – Kdark=(1. 9± 0. 6) 105 carriers/cm 3/sec per Me. V/g silicon (Srour 2000) current for • This is for one week after exposure – A = 6. 25*10 -6 cm 2 – = 2. 33 g/cm 3 – q = 1. 6*10 -19 C • For 50 krad exposure to 60 Me. V proton beam is ED is 16. 05 Me. V • Mean Dark Current = KDE ED = 33. 5 n. A/cm 2 at 300 K • Or, Mean Dark Current = 2. 25 f. A/pixel = 14000 e-/pixel/sec at -20 °C (one week after exposure) Cf. D 27

Test Hardware Cf. D 28

Test Hardware Cf. D 28

Conclusions • We have developed, and are testing, a 256 x 256 photon-counting imaging

Conclusions • We have developed, and are testing, a 256 x 256 photon-counting imaging array detector. • After lab characterization, we will expose four devices to radiation beam and then re-test. Cf. D 29

Detector Virtual Workshop • Year-long speaker series dedicated to future advanced detectors • Talks

Detector Virtual Workshop • Year-long speaker series dedicated to future advanced detectors • Talks streamed and archived • Email if interested in being on distribution list: figer@cfd. rit. edu Cf. D 30