Speaker
Description
Summary
The Pixel Detector R&D group at Fermilab has been developing a pixel detector to
meet the stringent requirements of the BTeV experiment. This pixel detector would
be composed of 60 pixel planes of approximately 100x100 mm2 each, assembled
perpendicular to the colliding beams and installed less than one centimeter from
the beam. The planes in the pixel detector are formed by sets of pixel-hybrid
modules of different lengths, each composed of a single active-area sensor tile and
of one row of readout integrated circuits (ICs).
The BTeV pixel detector module is based on a design relying on a hybrid approach.
With this approach, the readout chip and the sensor array are developed separately
and the detector is constructed by flip-chip mating the two together. This approach
offers maximum flexibility in the development process, the choice of fabrication
technologies, and the choice of sensor material.
The building block of the pixel detector is the pixel multichip module, which is
composed of three layers. The bottom layer is formed by a low mass high-density
interconnect (HDI). The back of the pixel readout IC is in thermal and electrical
contact with the HDI, while the top of the pixel readout IC is flip-chip bump-
bonded to the pixel sensor. The readout IC pads are wire-bounded to the HDI. The
large number of signals in this design imposes space constraints and requires
aggressive HDI design rules, such as four impedance-controlled signal layers with
50µm width trace and 50µm trace-to-trace clearance.
The pixel detector would be employed for on-line track finding in the lowest level
trigger system and, therefore, the pixel readout ICs would have to transmit data
for all detected hits. This requirement imposed a severe constraint on the design
of the readout IC, the hybridized module, and the data transmission to the data
acquisition system.
Recent characterization results of several preproduction pixel multichip modules
are presented in this paper. These preproduction modules were characterized for
threshold and noise dispersion using an analog test pulse injected into their
preamplifiers. The connectivity of the bump-bonds was tested using a radioactive
source (Sr90), and the absolute calibration of the modules was achieved using X-ray
sources. The pixel detector would be built at room temperature and operated at -5C,
implying a significant thermal variation. For this reason we characterized the
electrical and mechanical performance of the pixel module at different operating
temperatures ranging from -15C to 40C. Preliminary tests show that the
preproduction pixel module meets or surpasses the electrical and mechanical
requirements of the pixel detector for BTeV.
