Transcript Long Shaping-time Silicon Readout Bruce Schumm UC Santa Cruz Arlington Linear Collider Workshop January 9-11 2002

Long Shaping-time Silicon
Readout
Bruce Schumm
UC Santa Cruz
Arlington Linear Collider Workshop
January 9-11 2002
Participants
Dave Dorfan, Christian Flacco, Alex Grillo, Hartmut
Sadrozinski, Bruce Schumm, Abe Seiden, Ned Spencer,
Lan Zhang
Also, a new post-doc (Gavin Nesom) will probably
join the effort in February
Potential external associates: SLAC, LPNHE Paris,
CERN RD50
Motivation
Use of long shaping-time readout (low noise) plus exploitation
of duty cycle permits development
of very long, thin ladders
Additionally, limited readout and servicing may lead to
very limited material budget in forward region (down to
100 mrad)
Scope and Funding
Work funded via a two-year, $90,000 grant from
the DOE Advanced Detector R&D Program
(Will need to enter regular LC funding game afterwards)
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9 months graduate student support
Chip fabrication
Long-ladder development (existing sensors)
Electronics servicing to ladder
Detailed Scope
Given the duration and magnitude of the support, our
`deliverables’ will be
• Characterization of analog characteristics of 0.25
micron structures
• Development of pulse development and electronic
simulation for shaping-time and readoutscheme optimization
• Demonstration of noise level commensurate with
readout of 2m ladder
• Demonstration of x100 suppression of IR heating loss
• Min-i readout of 2m ladder
Pulse Development Simulation
Questions to be answered:
• Sensor geometry and analog resolution required
to achieve <7 um resolution
• Effect of large magnetic fields
• Effects of oblique angles of incidence
• Optimal detector bias
Pulse Dev Sim Cont’d
Effects considered so far:
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Landau fluctuations (SS_SIMSIDE, Jerry Lynch, LBNL)
Electron diffusion
Lorentz angle
Space-charge repulsion
Long Shaping-time Bail-out
Much of pulse simulation effort goes into `weightingfield’ calculation (pulse-development Green’s Fnc)
However, integral of total charge is
• e if electron hits strip
• 0 if electron misses strip
In t --> infinity limit, this is all you need to worry about!
Electron Diffusion
Electron diffusion distribution given by
 1 r2 
P(r , t )  exp 

2
D
t
q 

with diffusion constant given by
 kT 
Dq     q
 q 
Effect of B field?
Space-charge Effects
Model deposition as uniform line of charge of radius b
and linear charge density l.
After separation of electrons, holes, distribution expands
conformally:
l
s (t )  s0
t 1
2
 0 b
Other Simulation Aspects
For now, assume mobilizing field that of plane-biased
diode (obscures details of field near strips)
Variable inputs:
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Detector geometry (pitch, thickness)
Magnetic field
Track parameters
Detector bias
Potential Associations
Aurore Savoy-Navarro (LPNHE Paris)
Have discussed development of full-scale ladder,
readout for testbeam run
RD-50 (CERN, Mara Bruzzi)
Standing request for expert consultation (Lorentz
angle, diffusion and mobility vs. B, etc.)
Possible exploration of `Czochralski’ sensors (large
area, but leakage current needs work for now)
Next Six Months
Immediately: begin SPICE-level optimization of shaping
time (assuming 1-2 meter ladder)
Have already begun qualifying GLAST 8-channel `cutoff’
structures for use in 2m ladder
March: begin mechanical design and construction of
two-meter ladder
Submission of prototype ASIC in June
Longer Term
• Summer 2003: measure noise and power consumption
characteristics
• Fall 2003 (likely): begin design of 2nd prototype chip
based on accumulated experience
• Winter 2004: begin development of realistic prototype
ladder, prepare for testbeam run
• Summer 2004: testbeam studies; begin to develop
scheme for back-end architecture
NOTE: Project funded from DOE ADR program through
2003; afterwards, will need to switch to nominal sources!