1. in collaboration with Jamie Holder & Vladimir Vassiliev
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: Disadvantages:
- 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. Hybrid CMOS Detectors and Camera Readout, Abe Falcone
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. 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-Illuminated Back-Illuminated
Buried Channel
Thin oxide layer
Gate structures
Depleted Si
Depleted Si
Gate structures
Thin oxide layer
Hybrid CMOS Detectors and Camera Readout, Abe Falcone

6. Hybrid CMOS Detectors and Camera Readout, Abe Falcone
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
CTI
Hybrid CMOS Detectors and Camera Readout, Abe Falcone

7. 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

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

11. 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

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

13. Hybrid CMOS Detectors and Camera Readout, Abe Falcone
Hybrid CMOS H1RG-125 A
1016x451, 18mm pixel array
With Filter B
1016x565, 18mm pixel array
Without Filter
Optical image
55Fe X-ray image
Hybrid CMOS Detectors and Camera Readout, Abe Falcone

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

15. 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

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

17. 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

18. 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

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

20. 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