Hybrid cmos sensors and potential application to next generation vhe telescopes
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Hybrid CMOS Sensors and Potential Application to Next Generation VHE Telescopes. Abe Falcone Penn State University in collaboration with Jamie Holder & Vladimir Vassiliev. The Basic Idea: Fibers + II +CMOS.

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Hybrid CMOS Sensors and Potential Application to Next Generation VHE Telescopes

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Hybrid CMOS Sensors and Potential Application to Next Generation VHE Telescopes

Abe Falcone

Penn State University

in collaboration with Jamie Holder & Vladimir Vassiliev


The Basic Idea: Fibers + II +CMOS

System takes amplified pixel voltage to a fiber driver + fiber + gated image intensifier to a hybrid CMOS sensor

  • Relies on advances from past several years:

    • hybrid CMOS developed for fast (320 Mpix/sec) readout of select pixel regions

    • Fiber drivers and fibers have been developed to high standards for telecommunications (nsec response and <1% losses over >700 m)

    • Gated Image intensifiers are fast (2 nsec)

from Mirzoyan et al. 2000


Some Pros and Cons

Advantages:

- Replace heavy/thick cables with light/thin fibers

- Low cost readout (roughly $20-50 per channel)

- Readout of entire camera is done in one unit, thus making maintenance easier

- Very low power requirements

- Embedded CMOS electronics and readout ASIC tunable to our task (Note: This could even lead to event driven readout, which could eliminate need for image intensifier!)

Disadvantages:

- expensive upfront engineering... BUT much of this can be "piggy-back" on other development efforts at PSU

- entire waveform is not digitized


CCDs: Heritage

  • CCDs have been demonstrated on many existing X-ray missions (eg Chandra, XMM, Swift, Suzaku,...)

  • State of the art for:

    • low noise

    • high QE

    • moderate spectral resolution

    • excellent spatial resolution

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


X-ray CCDs

  • Photon detection

    • Photoelectric absorption in silicon, N=E/3.68 eV

    • Photo-charge drifts in electric field to buried channel

    • Gates are clocked to move charge packets to readout

      Front-IlluminatedBack-Illuminated

Buried Channel

Thin oxide layer

Depleted Si

Gate structures

Depleted Si

Gate structures

Thin oxide layer

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


CTI

X-ray CCDs

  • Photon detection

    • Charge splits between adjacent pixels due to spreading of charge cloud

    • Charge transferred in “bucket brigade” fashion

    • During transfer across CCD surface, some charge is lost in defects (traps), resulting in further spreading of charge into trailing pixels

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


X-ray CCDs

  • CCD advantages:

    • “Fano-limited” energy resolution, σrms~ (0.1Ne)1/2

    • Large-format devices with good spatial resolution

    • High quantum efficiency

    • Very linear behavior

  • CCD Disadvantages:

    • Energy resolution is only moderate

    • High sensitivity to radiation damage

    • Entire frames must be read out --> only moderate speed

    • Photon pileup at high count rates

  • Future missions (JANUS, Con-X, EDGE, possible upcoming rockets, ...) call for high throughput and a need to overcome pile-up and radiation limitations

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


The Future in Space: Hybrid CMOS

  • Random-access pixel readouts

  • Silicon-based devices:

    • Similarities to CCDs:

      • Photoelectric absorption in silicon

      • Energy resolution comparable to CCDs

      • Large arrays like CCDs

    • Low sensitivity to radiation damage (because charge is not transferred across the device

    • High count rate capability (random access allows arbitrary window readout vs entire device readout for CCD)

    • On-chip integration of signal processing electronics

--> Significant effort will be put into enhancing their capabilities, thus benefiting potential VHE application

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


Hybrid CMOS Detectors

  • Based on JWST technology, IR detectors

  • Back illuminated

  • random access readout

  • 1k x 1k, 2k x 2k, and 4k x 4k form factors

  • Detector array and readout array built separately, bump-bonded together

    • Allows separate optimization of

      detector and readout

    • Readout electronics for each pixel

    • Optical blocking filter on detector

  • Very high speed (10 Mpixel/sec x 32 outputs), low power device suitable for future high-throughput X-ray missions

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


Hybrid H1RG sensor

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


Hybrid CMOS in Lab

  • First-generation HCD device in PSU test camera

  • Designed for window readout mode

  • Readout speeds to 10 MHz

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


PSU Development Facilities

47 m Long Cell vacuum chamber

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


A

1016x451, 18mm pixel array

With Filter

B

1016x565, 18mm pixel array

Without Filter

Hybrid CMOS H1RG-125

Optical image

55Fe X-ray image

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


Hybrid CMOS H1RG-125

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


  • Future developments: on-chip CDS with high-speed, low-noise capacitive transimpedance amplifier:

  • Also working for on-chip event-driven readout

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


Hybrid CMOS Detectors - PSU

  • Implement ASIC camera controller

  • Camera control becomes software problem

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


Conclusions

  • Hybrid CMOS detectors are currently undergoing rapid growth for space-based instrumentation

  • This technology can also be exploited for ground based telescopes, including TeV arrays

  • At PSU, we are already developing this technology for other purposes --> minimal investment required to pursue VHE path

  • Current state of the art might achieve our goals cheaply and reliably; Future developments (speed, noise, event driven readout,...) could improve on this position

  • While traditional options may appear to be safer for building a telescope today, the potential of this technology should be explored for building a telescope tomorrow

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


The Swift X-Ray Telescope is just the latest example of the successful long-term hardware program in place at PSU

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


PSU Development Facilities

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


X-ray CCDs

  • X-ray CCDs are photon-counting detectors

  • Individual “events” must be extracted from bias level of CCD using short exposures

Hybrid CMOS Detectors and Camera Readout, Abe Falcone


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