Recent R&D Results on a Pixel Detector for Belle. Gary S. Varner University of Hawai, i SVD Upgrades October 23, 2000

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1 Recent R&D Results on a Pixel Detector for Belle Gary S. Varner University of Hawai, i SVD Upgrades October 23, 2000

2 Presentation Outline Sensor fabrication A dedicated Belle planar sensor has been in SNF for a few months Hopefully available in a month or two, personnel/equipment dependent XTEST2 Testing Brief review of concept Test results and problems Resubmission as XTEST2A, due early Nov. Bump-bonding Testing Global tender for thin, tight-pitch bump bonding (50x100um) results for 100µm,100µm sensor/electronics pairs new concepts for interconnect technology Thinning Thinned and Bumped Devices Results of tests Important enabling technology 1

3 Enabling Technologies: MEMS Micro-Electro- Mech Structures 2

4 Detector Results - sensitivity Slow amp. readout Excellent resolution Energy deposition largely contained within a single drift cell though electrodes of finite extent, efficient Q acq. 3

5 Results - Leakage Current Excellent performance at LHC doses: Respectable plateau at tolerable leakage current comparable ATLAS planar sensor difficult to deplete with 600V 4

6 Readout Electronics progress Gaining experience in design/test of XTEST2, a pixel upgrade effort: Pixel size # Pixel (total) Sensor thickness Constraints : Smallest pixel thin sensor low power Heat disp./ cell DELPHI 330x330µm 1.2M 300µm 40µW WA97 50x500µm 1.2M 300µm ATLAS 50x400µm 105M µm 50µW CMS 150µm 2 56M µm 60µW ALICE 50x300µm 15.7M 150µm 30µW BTeV 50x300µm 60M 300µm <40µW Belle 40x60µm 3.8M 100µm <1µW LC-PMpix 100x100µm 2.3M µm Exploring the envelope in small pixel readout 5

7 XTEST2 Design Concept Simple readout structure Decent performance w/o pre-amp (see below) Comparator powering during encoding 5-bit Wilkenson encoding (1mV/µs ~ 40µs) After encoding, fast LVDS data transfer out 6

8 Expected Performance Results for 100µm thick 7

9 Interconnect Concerns Excellent SNR and Timing However, interconnect issues: 8

10 XTEST2 Prototype Fabrication Radiation test structures 16x24 Array LVDS Driver 20µm bump pads Alignment Test 100 µm 50 µm 90µm 2 wire bond pads 5-bit Graycode Counter

11 XTEST2 Initial Prototype Gray-code Counter 16x24 Array of pixels: LVDS Drivers 100 µm Rad-test structures 50 µm To test feasibility, a prototype (XTEST2) was fabricated in HP0.5µm Jan-Apr 00 10

12 XTEST2 Test Set-up LVDS CPU ECL / 2366 XTEST2 chip 11

13 Problems 1: Gray-code Counter 12

14 Problems 2: LVDS Driver No connect HS LVDS test circuit also showed dynamic FF unexpected behavior, required redesign no obvious problems with LVDS driver itself 13

15 XTEST2 Radiation Results Radiation hardness consistent with T ox Quite adequate total dose performance 14

16 Comparator Performance 1M, 10pF load Active FET probe, 0.1pF load Performance better than expected decent switching low bias current good match to SPICE simulation 15

17 XTEST2 Performance Results Test Results: 2 of 3 analog issues comparator works LVDS/readout testing inhibited XTEST2A Submitted 8/7 better DRC/SPICE chips in early Nov. Complete LVS check 16

18 SPICE Sim.: front-to-back 17

19 XTEST2A Encoding 18

20 Bump Bonding Tests Global tender: only 2 companies willing to work with thin devices: AIT (Hong Kong) GEC-Marconi (U.K.) GEC withdrew ARO Concern for LHC community also Bonded both 300µm and 100µm thick devices 19

21 Bump Bonding Results (1) Sample measurement : 20

22 Bump bonding Results(2) 21

23 Bump bonding Summary Problems encountered with 50x100µm Loose Indium? Bad UBM? misalignment Probably no problem for 100x100µm We continue to seek other solutions 22

24 Thinning bumped: Edge guard Utilize Xe-F etcher to thin If can protect the sides (e.g. with photoresist), metal/others OK 23

25 Thinning (after bonding) Utilize Xe-F etcher to thin Initial tests leave room for improvement in uniformity, but solutions being sought: 24

26 Thinning Thickness Summary Despite some problems with uniformity Allows bump-bonding of thick devices Can thin electronics extremely thin uniformity problems may have easy solution 25

27 Thinning Summary Despite some problems with mechanical uniformity No obvious changes to electrical properties Any changes probably due to mis-handling 26

28 Summary R&D into technologies proceeding well: Have established Radiation tolerant processes for both sensor and readout electronics Many basic issues addressed with XTEST2 Developing experience at handling interconnect issues Plans Sensor prototype available in 1-2 months Next version readout electronics (XTEST2A) ready for test in about a month first prototype system mid next year 27