The Silicon Tracker Readout Electronics of the Gamma-ray Large Area Space Telescope Marcus Ziegler

1. Gamma-ray Large Area Space Telescope The Silicon Tracker Readout Electronics of the Gamma-ray Large Area Space Telescope Marcus Ziegler Santa Cruz Institute for Particle Physics University of California at Santa Cruz GLAST LAT Collaboration ziegler@scipp.ucsc.edu

2.  e– e+ GLAST LAT Tracker Overview • The LAT Tracker is divided into: • 16 Tracker Towers • Each stack is composed of 19 trays. • Tray: • Carbon-composite panel • Si-strip detectors on both sides • On the bottom side of the tray, is glued an array of tungsten foils. • Adjacent trays are rotated by 90o, with a 2mm gap in between, to form an x,y measurement plane.

3. One Tracker Tower Requirements for GLAST: Power < 200 mW/channel Efficiency > 98% Noise occupancy < 5x10-5 Self triggering Trigger rate up to 10 kHz Minimal dead area Minimize single point failures

4. Characteristics of the Si-Tracker • 9126 Si-strip detectors from 6” wafers • 74 m2 of Si (228mm pitch) • 884 736 readout channels • 160 Watt power consumption

5. Readout Schema • 9 MCMs per side of the tower and 24 GTFE chips per MCM board • All front end chips can be programmed at any time from both sides • The layer OR is used as a trigger primitive (6 layer in a row form the usual tracker trigger) • The strip hits can be latched in one of the four GTFE readout buffers and be read out to both sides • Measure of the deposited charge by counting the clock ticks the layer OR is high

6. Right Angle Interconnect

7. Polyswitch Omnetics connector GTRC ASIC Pitch-adapter flex circuit with 90° radius GTFE ASIC Detail of an MCM, at One End

8. Mechanical Challenges Encapsulation Fill Encapsulation Dam Wire Bond Flex Circuit ASIC and Conductive Glue Fiberglass Riser Internal Cu Planes Fiberglass • X-ray cross section of the edge of the MCM with the right angle interconnect. • 1-layer Kapton flexible circuit that is glued over 1mm radius machined into the edge of the polyimide-glass PWB.

9. System Performance Power consumption: A low (<200 mW / channel) power consumption was achieved by keeping the amplification and digitization schemes very simple. → The power consumption of a typical tracker tower during data taking is measured to be 9.9 W Noise Performance: The shaper output peaking time is about 1.5 ms. For 36 cm long Si strips (about 41 pF load) the noise charge is about 1500 electrons. The most probable signal is 32,000 electrons for a MIP passing through 400 mm silicon. Noise Occupancy: The average fraction of channels above threshold at any snapshot in time. For a typical integrated tracker module we measured a noise occupancy of 4.7x10-7

10. Detection efficiency The fraction of active area within one plane of 16 SSDs is 95.5 % Taking into account the dead area between the towers the active fraction of the over all tracer is 89.4 % Hit efficiency The overall efficiency was measured for each layer using cosmic-ray tracks. We obtained efficiencies for the individual towers of about 99.6% Inefficiency comes from dead channels and low fluctuations in the ionization.

11. Photon event

12. Current status All 16 tracker towers (TKR and CAL) are installed into the lat (next is ACD) LAT integration completion in Jan 2006 Environmental testing at NRL until June 2006 Launch in August 2007