Ashra Report: Hybrid Photo Pixel Detector as the Trigger Sensor

1. Ashra Report:Hybrid Photo Pixel Detector as the Trigger Sensor Masataka Masuda (Tokyo Institute of Technology) for Ashra collaboration 31 Oct 2006, DPF2006

2. Ashra Collaborators Y. Aitaa, T. Aokia, Y. Asaokaa, T. Browderi, T. Chonana, S. Dyei, M. Eguchia, R. Foxh, S. Fukagawab, G. Guilliani, J. Hamiltonh, M. Ieirie, T. Kimurac, N.Kohtaf, I. Kogab, H. Kuzeb, J. Learnedi, N. Managoa, M. Masudag, S. Matsunoi, Y. Morimotof, K. Nodaa, S. Ogawaf, A. Okumuraa, S. Olseni, M. Sasakia, H. Shibuyaf, N. Sugiyamad, M. Yasudag, G. Varneri , Y. Watanabeg, Y. Watanabef (a) ICRR, Univ. Tokyo (b) Chiba Univ. (c) Ibaraki Univ. (d) Nagoya Univ.(e) KEK (f) Toho Univ. (g) Tokyo Inst. Tech. (h) Univ. Hawaii Hilo(i) Univ. Hawaii Manoa

3. Contents • Introduction • Image Pipeline of Ashra detector • Hybrid Photo Pixel Detector • CMOS Fine Sensor • Summary

4. Introduction: Ashra Detector • Distinctive Features: • 12 detectors/station All-sky Survey 2πsr80% • FOV / detector 0.42sr • High resolution a few arcmin • Hybrid detection • U.V., Cherenkov and fluorescence lights Self-trigger system for hybrid detection • Signal delay with slow decaying phosphor screen • Pattern recognition in Trigger sensor • Fine sensor withlocalexposure and readout

5. Pilot Observation of Cherenkov Showers Proton Shower Candidate Exposure: 200ns Each spot corresponds to individual incoming photon. Succeeded in self-triggering with almost final setup For wide FOV, technical developments are required for trigger.

6. Image Pipeline of Ashra detector Distributes same image to 4 sensors keeping good resolution and brightness with I.I.s, splitters and optical fibers. Untriggerd image sensor 20inch UV I.I. 1 Amp I.I. Fine Sensor Half mirror Delay I.I. Delay I.I. 4 Optical Fiber Afterglow sustains ~200ns Photon Trigger Sensor 2 3 electron Cerenkov fluorescence • Requirements for trigger sensors • trigger judgement within ~200ns • high resolution to recognize AS image • =>Hybrid Photo Pixel Detector 200ns

7. Hybrid Photo Pixel Detector  LSI chip Prototype Focusing Electrodes e- VACUUM Photocathode 6inch Silicon detector 307mm Electron tube, silicon pixel detector and readout LSI circuits Main features • De-magnification by ~ 5 • 6464 pixel silicon anode (450m450m each) • Trigger LSI chip for fast pattern recognition • Bump bonding and vacuum feedthroughs High resolution and Fast response are required

8. Simulation of electron trajectories Electron Trajectories Radial height (mm) electrodes Distance from the input surface (mm) Electron trajectory simulation • Optimize shape of input window, positions of electrodes and high voltages applied to them We simulated Point spread of photoelectons on the silicon detector

9. Simulated Point spread on silicon detector Meridional direction Input radius Sagittal direction Input window Point spread as a function of input radius Definition:Meridonal and sagittal direction Meridional 0.45mm line (pixel size) Sagittal Full width including 84% of photoelectrons << Pixel size of silicon detector (0.45mm) at any input radius Electron tube with high resolution is designed. 0.45mm line (pixel size)

10. Silicon Pixel Detector Rear • Technical features • Simple p+ n type • Depletion voltage 65-105V • Electron collection for fast response • 6464 pixel array • (Number of pixels is maybe largest! ) • Bump bonded to LSI readout chips • Crosstalk, Response and Dark currents are simulated. n+ h+ e- 250µm h+ e- n-sub h+ e- sectional view p+ e- 450µm Front 20µm 430m 6464 PAD 28840µm 30800m 28840µm surface 30800m

11. Electric fields and Currents in Silicon Detector Local electric field concentration => Currents increase with avalanche Designed carefully to prevent avalanche breakdown. Dark current of 0.3nA/pix. << Signal current ~ a few A (1TeV Gamma ray)

12. Crosstalk and Response in Silicon detector Electrode Simulation ・Electric fields in 33 pixels ・ Electrons trajectories ・Drift time of electrons Results ・Crosstalk ~ 0 trajectory // z direction ・Fast responce drift time ~ 6ns Trajectory h+ e－ e－ -100V Silicon detector with low crosstalk is well designed.

13. Trigger LSI circuits 9.8mm 9.8mm 16x16 discriminator array equipped on the back of HPD Circuit Diagram of a pixel • Characteristics • Each pixel consists of I-to-Vconverter, filter and comparator. • Time constant can be changed. • Threshold voltage can be changed with control signal. Response in Trigger LSI was measured.

14. Timing Test of Trigger LSI Circuit board for Trigger LSI Output 50ns Input Input: 200ns Pulse Output Scope Pulse Gen. LSI DCV threshold LSI chip with BGA Typical delay time in each pixel = 50ns < Delay I.I. afterglow sustains for ~ 200ns 9.8mm

15. Exposure and Readout Control of CMOS Sensor 1. Signal hits pixels in trigger LSI 2. Output X and Y Wired- OR trigger pulses 3. Address the region in Fine sensor 4. Start exposure and hold Q 5. Repeat 1~4 with overlapping 6. Finally take AS image with any duration and at any time

16. CMOS fine sensor • Standard CMOS process • 2-poly3-metal0.35µm • Chip size 1919mm • Number of Cells 128128 • Pixels in the Cell 1616 • Number of pixels 20482048 • Pixel size 88µm • Readout 12.8s/Cell • Trigger rate (Proton Cherenkov BG) ~ 1kHz • Exposure and readout for each cell

17. Imaging with CMOS Fine Sensor X-Trigger Ashra CMOS Sensor Control Signals Y-Trigger A/D Converter Personal Computer CMOS Sensor F-Mount Processor Board • An Image was focused onto the CMOS sensor • Processor board generates trigger signal and selects readout cells. Succeeded in obtaining image with 100ns exporsure

18. Summary and future plans Hybrid Photo Pixel Detector / Electron tube and silicon detector are well designed. High resolution, fast response and low crosstalk are simulated. / Readout LSI circuit has been developed. Response time of 50 ns was measured. CMOS fine sensor has beed developed Image with 100 ns exposure is obtained. Silicon pixel detector is scheduled for completion in next December. Self-trigger with HPD and CMOS sensor will be coming soon.