May 2000 Radiation Tolerant Version of the VA1 1 A Radiation Tolerant Version of the VA1 FEE2000 Perugia, Italy Daniel Marlow Princeton University May 16, 2000

May 2000 Radiation Tolerant Version of the VA1 2 Introduction The BELLE collaboration is in a special situation, wherein export restrictions and limited resources make it difficult to gain access to bona fide rad- hard IC processes. Our radiation-tolerance requirements are modest, lying in the few hundred kRad to few MRad range. The BELLE SVD development followed an “unusual” history, wherein we were obliged to make a last-moment switch to an established (non- rad-hard) design, namely the VA1.

May 2000 Radiation Tolerant Version of the VA1 3...Introduction Although this has at times been a difficult journey, it has afforded us an opportunity to carry out a systematic study of the effect of line-width on a practical design. Specifically, we have measured the radiation tolerance of the VA1 chip for the following three CMOS processes: –AMS 0.8 um –AMS 1.2 um –AMS 0.35 um The differences between the designs and processes (apart from feature size) are as small as possible.

May 2000 Radiation Tolerant Version of the VA1 4 Outline The Team BELLE & KEK-B The BELLE SVD The VA1 Chip Readout Architecture Radiation Levels at KEK-B Basic Idea Results Summary & Conclusions

May 2000 Radiation Tolerant Version of the VA1 5 The Team IDEAS (Oslo, Norway): –S. Mikelson, E. Nygård, J. Talebi University Of Hawaii –G. Varner KEK –M. Tanaka, T. Tsuboyama Princeton University –DRM University of Tokyo –H. Tajima, M. Yokoyama

May 2000 Radiation Tolerant Version of the VA1 6 A Special Thanks... BELLE SVD Review Committee(s): P. Weilhammer (chair) Members: J. Alexander (Cornell), W. Dabrowski(Krakow), R. Horisberger (PSI) K.T. Knoepfle (Heidelberg) H. Spieler (LBL) N. Uno (KEK)

May 2000 Radiation Tolerant Version of the VA1 7 Physics Mission Statement tag CP Our principal physics goal is the observation of indirect CP violation in decays.

May 2000 Radiation Tolerant Version of the VA Physics Mission Statement The time-dependent asymmetry appears mainly as a mean shift in the distribution between events tagged as decays and events tagged as decays.

May 2000 Radiation Tolerant Version of the VA1 9 The KEK-B Asymmetric Collider KEK-B is similar to PEP- II in many ways, although there is a (potentially) important difference in the way in which the beams are brought into collision.

May 2000 Radiation Tolerant Version of the VA1 10 KEK-B Performance Integrated Luminosity Typical Daily Luminosity

May 2000 Radiation Tolerant Version of the VA1 11 Recent Run Snapshot

May 2000 Radiation Tolerant Version of the VA1 12 The Magnet BELLE Collaboration: 250 physicists 50 Institutes 10 countries

May 2000 Radiation Tolerant Version of the VA layers Delphi-style DSSDs from HPK VA1 analog readout The BELLE SVD (V1.0)

May 2000 Radiation Tolerant Version of the VA1 14 The VA1 Chip 128 channels Descendent of Viking (O. Toker et al., NIM A340 (1994) 572.) AMS 1.2 um CMOS Noise:

May 2000 Radiation Tolerant Version of the VA1 15 VA1 Principle of Operation Classic track and hold architecture VA1 shaping time provides latency for Level 1 trigger. 10 MHz Serial analog readout.

May 2000 Radiation Tolerant Version of the VA m30 m Repeater SystemHybridsDSSDs On Detector Near Detector Electronics Hut HALNY FADC System /4 of System 20,280 channels. VA1 Chips System Block Diagram

May 2000 Radiation Tolerant Version of the VA1 17 HALNY FADC Board

May 2000 Radiation Tolerant Version of the VA1 18 The HALNY is a 6U VME Module Developed by INP Cracow

May 2000 Radiation Tolerant Version of the VA1 19 System Performance candidate

May 2000 Radiation Tolerant Version of the VA1 20 SVD Performance Bhabha miss distance

May 2000 Radiation Tolerant Version of the VA1 21 SVD Performance

May 2000 Radiation Tolerant Version of the VA1 22 Physics Results: Charm Lifetimes

May 2000 Radiation Tolerant Version of the VA1 23 Neutral B Mixing

May 2000 Radiation Tolerant Version of the VA1 24 Now the Bad News... We see a drop in gain over time, which is consistent with what we expect from the measured dose. The 1.2-micron VA1s are projected to die after about 10 fb -1 (c.f. initial goal of 100 fb -1 ).

May 2000 Radiation Tolerant Version of the VA More Bad News In June of 1999 we noticed a sudden decrease in gain of the inner layer VA chips. The problem was ultimately found to be a large flux of low-energy x-rays.

May 2000 Radiation Tolerant Version of the VA More Bad News Although we could easily solve the x-ray problem, it’s hard to anticipate every possible problem. Greatly improved radiation-hardness is clearly needed.

May 2000 Radiation Tolerant Version of the VA1 27 Why AMS? Export restrictions are a headache for Japan. Limited access to IC designers. Limited funds. Tight schedule. Familiarity with the VA1. Existing readout system. The other options we studied had their own uncertainties.

May 2000 Radiation Tolerant Version of the VA1 28 Something even a physicist can understand... depends on ionization Reducing the oxide thickness by half is equivalent to cutting the dose by four.

May 2000 Radiation Tolerant Version of the VA1 29 AMS Process Comparison Feature Size Projected Tolerance 1.2 μm250 Å200 kRad 0.8 μm160 Å500 kRad 0.6 μm125 Å800 kRad 0.35 μm75 Å2200 kRad

May 2000 Radiation Tolerant Version of the VA1 30 Test Conditions University of Tokyo (M. Yokoyama) 60 Co gamma source 1 kRad/min ICs powered during irradiation. Bias parameters adjusted for best performance with each measurement. Independent measurements at Univ. of Hawaii confirmed Tokyo results.

May 2000 Radiation Tolerant Version of the VA1 31 Original VA1 Test Results AMS 1.2 um CMOS

May 2000 Radiation Tolerant Version of the VA1 32 Original VA1 Test Results AMS 1.2 um CMOS

May 2000 Radiation Tolerant Version of the VA1 33 AMS 0.8 um CMOS

May 2000 Radiation Tolerant Version of the VA1 34 AMS 0.8 um CMOS

May 2000 Radiation Tolerant Version of the VA1 35 Process Comparison In the range of interest to BELLE, the noise performance dramatically improves with decreasing feature size, as expected.

May 2000 Radiation Tolerant Version of the VA1 36 Indeed, the 0.35-um process exhibits phenomenal radiation hardness.

May 2000 Radiation Tolerant Version of the VA1 37 Comments on Power Consumption Guard rings were not added to the design. We did not observe a significant increase in current consumption after irradiation. We believe that this is because the current draw is dominated by analog circuits, which already have large per-transistor currents.

May 2000 Radiation Tolerant Version of the VA1 38 AMS Process Comparison Feature Size Projected Tolerance Observed Tolerance 1.2 μm250 Å200 kRad 0.8 μm160 Å500 kRad1200 kRad 0.6 μm125 Å800 kRad*** 0.35 μm75 Å2200 kRad> 20 MRad

May 2000 Radiation Tolerant Version of the VA1 39 Conclusions We have developed a version of the VA1 chip exhibiting good radiation tolerance. Radiation hardness improves with decreasing feature size, as expected. The naive expectation of scaling of the radiation hardness is significantly exceeded.