BTeV Pixel Detector Research Articles

The BTeV Pixel Detector

We present the current status of the BTeV pixel detector. The BTeV pixel detector will consist of 23 million pixel elements housed within the vacuum system of the Fermilab Tevatron within 6 mm of the beams, retracting to > 20 mm during beam injection. The pixel detector will operate in a 1.6 T dipole field, providing vertex, tracking and modest stand-alone momentum measurements to the level 1 trigger system. We focus on the unique mechanical, thermal and vacuum issues related to this detector system.

Study of temperature dependence of bump bonding for the BTeV pixel detector

The pixel detector proposed for the BTeV experiment at the Fermilab Tevatron will use bump-bonding technology based on either Indium or Pb/Sn solder to connect the front-end readout chips to the silicon pixel sensors. We have studied the behavior of the bumps by visual inspection of the bumps bonding silicon sensor modules to dummy chips made out of glass. The studies were done before and after thermal cycles, exposure to intense irradiation, and with the assemblies glued to a graphite substrate. We have also carried out studies on effects of temperature changes on both types of bump bonds by observing the responses of single-chip pixel detectors to a /sup 90/Sr source. We report the results from these studies as well as the noise and threshold behavior of the pixel readout at various temperatures.

The BTeV pixel detector and trigger system

BTeV is an approved forward collider experiment at the Fermilab Tevatron dedicated to the precision studies of CP violation, mixing, and rare decays of beauty and charm hadrons. The BTeV detector has been designed to achieve these goals. One of the unique features of BTeV is a state-of-the-art pixel detector system, designed to provide accurate measurements of the decay vertices of heavy flavor hadrons that can be used in the first trigger level. The pixel vertex detector and the trigger design are described. Recent results on some of the achievements in our R&D effort are presented.

Development of a readout technique for the high-data-rate BTeV pixel detector at Fermilab

The pixel detector for the BTeV experiment at Fermilab provides digitized data from approximately 22 million silicon pixel channels. Portions of the detector are 6 mm from the beam, providing a substantial hit rate and high radiation dose. The pixel detector data will be employed by the lowest level trigger system for track reconstruction every beam crossing. These requirements impose a considerable constraint on the readout scheme. This paper presents a readout technique that provides the bandwidth that is adequate for high hit rates, minimizes the number of radiation-hard components, and satisfies all other design constraints.

Development of a high density pixel multichip module at Fermilab

At Fermilab, both pixel detector multichip module and sensor hybridization are being developed for the BTeV experiment. The module is composed of three layers. The lowest layer is formed by the readout integrated circuits (ICs). The backs of the ICs are in thermal contact with the supporting structure, while the tops are flip-chip bump bonded to a pixel sensor. A low mass flex-circuit interconnect is glued on the top of this assembly, and the readout IC pads are wire-bonded to the circuit. The BTeV pixel detector is based on a design relying on this hybrid approach. This method offers maximum flexibility in the development process, choice of fabrication technologies, and the choice of sensor material. This paper presents strategies to handle the required data rate and performance characteristics of the pixel module prototypes.

PreFPIX2: core architecture and results

PFIX is a pixel architecture designed for colliding-beam experiments at the Tevatron. Its most important application to date is the BTeV experiment. PreFPIX2 is a chip designed to test the FPIX Core, i.e., the pixel control and readout architecture. This FPIX Core will be mated to a periphery specific to a particular experiment. Earlier plans called for the BTeV FPIX chip to be designed in a rad-hard process. However, deep-submicron CMOS processes have demonstrated appropriate radiation tolerance at a lower cost and with greater reliability. Therefore, PreFPIX2 has been fabricated in a 0.25 micrometer process utilizing radiation tolerant design techniques. The architecture has undergone substantial development from earlier versions of FPIX. Most notable are the improvements to the column token passing scheme and to the end-of-column logic. Extensive simulations were performed using both SPICE and structural-level Verilog. Monte Carlo physics simulations of the BTeV pixel detector at half, full and double the planned luminosity were converted to Verilog compatible input files for the chip simulations, allowing the designers to observe the chip operating under real conditions and for extended periods of time. Analyzes of the results reveal that at all luminosities the FPIX Core correctly identifies better than 99.6% of input hits. Bench tests of fabricated chips confirm the accuracy of the simulations.

The development of software to characterize the Fermilab pixel readout chip, FPIX1, for the BTeV experiment

Fermilab has designed and assembled a pixel-readout-chip sub-assembly containing five FPIX1 chips with flexible cable interconnections with which to address the technical issues involved in system integration for the proposed BTeV pixel detector. The module contains a total of 14 400 pixel cells that need to be characterized in order to test the entire module. Software has been developed within the LabVIEW framework to control a set of instruments to perform threshold and noise tests on all five readout chips. These tests take only a few hours to run.

The BTeV pixel detector and trigger system

BTeV is a collider experiment approved to run at the Tevatron at Fermilab. The experiment will conduct precision studies of heavy flavor decays, with particular emphasis on CP violation, flavor oscillations and rare decays. One of its unique features is a state-of-the-art pixel detector system, designed to provide accurate measurements of the decay vertices of heavy flavored hadrons to be used in the first trigger level. This will enable BTeV to study beauty and charm decays to unprecedented precision. The key features of the pixel vertex detector and the trigger design are reviewed. Some beam test data with prototype pixel sensor and front end-electronics are reported. They are compared with our Monte Carlo simulation predictions.