Hybrid CMOS Sensors and Potential Application to Next Generation VHE Telescopes

1. Hybrid CMOS Sensors and Potential Application to Next Generation VHE Telescopes Abe Falcone Penn State University in collaboration with Jamie Holder & Vladimir Vassiliev

2. 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

3. 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

4. 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

5. 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-Illuminated Back-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

6. 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

7. 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

8. 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

9. 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

10. Hybrid H1RG sensor Hybrid CMOS Detectors and Camera Readout, Abe Falcone

11. 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

12. PSU Development Facilities 47 m Long Cell vacuum chamber Hybrid CMOS Detectors and Camera Readout, Abe Falcone

13. 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

14. Hybrid CMOS H1RG-125 Hybrid CMOS Detectors and Camera Readout, Abe Falcone

15. 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

16. Hybrid CMOS Detectors - PSU • Implement ASIC camera controller • Camera control becomes software problem Hybrid CMOS Detectors and Camera Readout, Abe Falcone

17. 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

18. 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

19. PSU Development Facilities Hybrid CMOS Detectors and Camera Readout, Abe Falcone

20. 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