BTeV Pixel Detector Status

Overall, the technical design and prototyping of the first four components is quite advanced. Work to solve the engineering issues on the last two components is now making good progress as well. More detailed discussion of the status of each of thesse sub-components can be seen below and obtained by "clicking" on the relevant item in the list above. Clicking on the links above will give the past status summaries as well as the current one (updated October, 2003).

Clicking on the above line will lead to a list of selected papers on the BTeV pixel system, with links to each paper.

Prototype sensors using p-stop isolation have been purchased and bench-tested before and after irradiation to 37 MRad (~1 x 10^15 MIPs). The first BTeV full-size, p-spray-isolation sensors have been received and bench-tested. This includes single-chip-size devices and various multi-chip-size devices (4, 5, 6, and 8 readout chips) for test. Beam tests to study charge collection and resolution before and after irradiation will be started when test beam is available at the Fermilab Meson Test Beam Facility where equipment is already installed.

We have also received p-spray sensors from the ATLAS collaboration. These have been bench tested before and after irradiation (up to 4x10**14 p/cm2). We also now have fifteen wafers using p-spray isolation and made to match the new FPIX2 chip. Bench tests show good yield, with leakage current and breakdown voltage meeting the BTeV performance specifications.

So far, it appears that both p-stop and p-spray sensors will operate at an acceptable level for ten years at design luminosity. Un-irradiated prototype devices achieved the required resolution in 1999 beam tests, and matched the expectations based on simulations. The plan is to test both p-stop and p-spray sensors in a test beam at Fermilab starting in the late fall of 2003.

The development of the BTeV readout chip is nearing completion. A series of tests of prototype chips implemented in two different commercial 0.25 micron CMOS processes have verified the functionality of all of the circuit blocks that make up the readout chip. Devices have been irradiated to 87 Mrad (~3 x 10^15 MIPs), a much higher dose than expected in ten years of running. This dose resulted in minimal threshold shifts and only minor changes to noise level. The rate of single-event upsets has been measured and proven to be well within acceptable limits.

Twenty-two 8-inch wafers of full-size "FPIX2" readout chips, including essentially all of the features envisioned for the final device, were received in January 2003. Tests performed in February indicate that the chip operates as designed. A large number of FPIX2 readout chips will soon be bump-bonded to sensors of various sizes and tested both on the bench and in a test beam at Fermilab.

Two types of bump-bonding technology are under investigation: indium and flux-less solder. Indium has been used so far on the prototype devices. We have started bench tests of solder bumped hybrids. We will use both types in the beam tests. Both technologies appear to have acceptable yield and robustness. Large-scale thermal-cycle tests have been performed on both indium and fluxless-solder bump-bonded devices. We have also studied the effects of irradiation and gluing to Thermal Pyrolytic Graphite (TPG) support material. Only small changes were observed. The preliminary conclusion is that while both indium and fluxless solder are viable techniques, solder bumps appear more robust so far.

Prototype HDIs have been received from CERN. Chip control and data output have been exercised through these devices with little effect on noise or other bench-test operation. A first five-chip detector module has been successfully tested with a radioactive source. Work is progressing to include this device in the test beam. Work has also started on the layout of the new HDI for the FPIX2-based modules. Potential vendors for production HDI orders have been contacted. The connection from the HDI to the outside of the pixel detector system will have separate signal and power cables to better optimize the conductor to insulator ratios. Lifetime testing of a prototype HDI flexible cable suggests that the BTeV design is adequate far beyond the number of flexing cycles anticipated for the detector.

The pixel detector will be located in the machine vacuum of the Tevatron. In order to determine the vacuum pumping requirements, a mechanical model of a number of pixel planes was constructed using most of the materials and construction methods envisioned for the final system. Measurements made using this "5%" model show that a suitable vacuum can be obtained if a combination of cryogenic panels using liquid nitrogen and cryogenic pumps using liquid nitrogen and helium are used.

Our previous design of the cooling and support structure has a large number of cooling joints. There are serious concerns on the potential leaks and their impact on the operation of the Tevatron. To address these problems, we are will use a joint-free design. Our new baseline will use Thermal Pyrolytic Graphite (TPG) which has excellent thermal conductivity.

The cryo panels introduced for vacuum purposes will be cooled by liquid nitrogen. A liquid nitrogen cooled heat sink will also be used to remove the heat generated by the pixel readout chips. By varying the thickness and width of a Thermal Pyrolytic Graphite (TPG) support, we have demonstrated by Finite Element Analysis that the operating temperature of the detector can be kept quite uniform and below 0 degree C everywhere. Prototyping work has also started on actual pieces of TPG and on flexible joints for connecting the TPG to outer supports using Pyrolytic Graphite Sheet (PGS). A number of dummy silicon modules are being assembled for placement on a TPG substrate. Thermal profiles and mechanical displacements will be measured, and compared to finite element analysis.

[ Fermilab at Work ] [ BTeV Home ] [ BTeV for Physicists ] [ BTeV Search ]

Send questions about the pixel status web pages to Jeffrey A. Appel.

This page last updated: Friday, 03-Oct-2003 13:13:20 CDT