Sherwood Parker

3D - A proposed new architecture for solid-state radiation detectors'

A proposed new architecture for solid-state radiation detectors using a three-dimensional array of electrodes that penetrate into the detector bulk is described. Proposed fabrication steps are listed. Collection distances and calculated collection times are about one order of magnitude less than those of planar technology strip and pixel detectors with electrodes confined to the detector surface, and depletion voltages are about two orders of magnitude lower. Maximum substrate thickness, often an important consideration for X-ray and gamma-ray detection, is constrained by the electrode length rather than by material purity or depletion-depth limitations due to voltage breakdown. Maximum drift distance should no longer be a significant limitation for GaAs detectors fabricated with this technology, and collection times could be much less than one nanosecond. The ability of silicon detectors to operate in the presence of the severe bulk radiation damage expected at high-intensity colliders should also be greatly increased.

Silicon detectors with 3-D electrode arrays: fabrication and initial test results

The first three-dimensional detectors with n and p electrodes that penetrate through the silicon substrate have been fabricated. Some expected properties, including low depletion voltages, wide voltage plateaus before leakage current limits are reached, and rapid charge collection are reviewed. Fabrication steps and initial test results for leakage currents and infrared signal detection are covered. The authors conclude with a description of current work, including fabrication of active-edge detectors, ones with sensitive areas that should extend to their physical edge.

Development of high density readout for silicon strip detectors

Abstract A compact readout for silicon strip detectors is being developed. It employs an nMOS circuit with 128 channels of charge sensitive amplifiers and multiplexed output.

Results from 3-D silicon sensors with wall electrodes: near-cell-edge sensitivity measurements as a preview of active-edge sensors

Silicon sensors with a three-dimensional (3-D) architecture, in which the n and p electrodes penetrate through the entire substrate, have been successfully fabricated. The electrode spacing can be less than the substrate thickness, allowing short collection paths, low depletion voltages, and large current signals from rapid charge collection. This paper gives results when the cylindrical electrodes of the earlier papers are replaced by a combination of cylindrical and wall electrodes-ones in which a trench, rather than a hole, is filled with doped polycrystalline silicon. The detection efficiency remains high to within a few micrometers of these wall electrodes, and is an indication that similar high efficiencies should be achievable near the physical edges of the proposed active-edge sensors.

The experimental identification of individual particles by the observation of transition radiation in the x-ray region

Abstract Transition radiation in the X-ray region produced by 1.3 GeV/c and 3.0 GeV/c electrons has been detected using multi-wire proportional chambers (MWPC). The radiation was generated in eleven stacks of 100 mylar foils (thickness 1 2 mil. or 1 6 mil. ) each preceding one of eleven MWPC placed in line; two inch thick slabs of styrofoam were also used. The incident particles, electrons or π−-mesons, passed through the MWPC as well as the foils. Results are given on the numbers of transition radiation photons detected, the energy deposition in the chambers and the relativistic rise of ionisation loss in argon and krypton. The distribution in total pulse height obtained with krypton shows a good separation of π−-mesons and electrons at 3 GeV/c.

First results from a silicon-strip detector with VLSI readout

Abstract A 256-strip silicon detector with 25 μm strip pitch, connected to two 128-channel NMOS VLSI chips (Microplex), has been tested using straight-through tracks from a ruthenium beta source. The readout channels have a pitch of 47.5 μm. A single multiplexed output provides voltages proportional to the integrated charge from each strip. The most probable signal height from the beta traversals is approximately 14 times the rms noise in any single channel.

A proposed VLSI pixel device for particle detection

Abstract A new form of silicon particle detector that has pixels composed of PIN diodes and readout circuits integrated on a common silicon substrate is described. Detected charge is isolated, and remains on a control gate during readout. Sparse field techniques permit the rapid readout of hit channels without the need for reading a large number of empty ones.

First beam test results from a monolithic silicon pixel detector

Abstract We have tested a telescope of four monolithic pixel detectors in a 300–600 GeV muon beam at Fermilab. The detectors were 300 μm thick and had 30 × 10 pixels of 34 by 125 μm2. The signal to single channel noise was 55 to 1 in the beam test. The position resolution in the 34 μm direction had a σ = 2.2 μm. In an efficiency test the detectors did not miss any of 2665 minimum ionizing particle hits.

First fabrication of full 3D-detectors at SINTEF

3D-detectors, with electrodes penetrating through the entire substrates have drawn great interests for high energy physics and medical imaging applications. Since its introduction by C. Kenney et al in 1995, many laboratories have begun research on different 3D-detector structures to simplify and industrialise the fabrication process. SINTEF MiNaLab joined the 3D collaboration in 2006 and started the first 3D fabrication run in 2007. This is the first step in an effort to fabricate affordable 3D-detectors in small to medium size production volumes. The first run was fully completed in February 2008 and preliminary results are promising. Good p-n junction characteristics have been shown on selected devices at the chip level with a leakage current of less than 0.5 nA per pixel. Thus SINTEF is the second laboratory in the world after the Stanford Nanofabrication Facility that has succeeded in demonstrating full 3D-detectors with active edge. A full 3D-stacked detector system were formed by bump-bonding the detectors to the ATLAS readout electronics, and successful particle hit maps using an Am-241 source were recorded. Most modules, however, showed largely increased leakage currents after assembly, which is due to the active edge and p-spray acting as part of the total chip pn-junction and not as a depletion stop. This paper describes the first fabrication and the encountered processing issues. The preliminary measurements on both the individual detector chips and the integrated 3D-stacked modules are discussed. A new lot has now been started on p-type wafers, which offers a more robust configuration with the active edge acting as depletion stop instead of part of the pn-junction.

PIN detector arrays and integrated readout circuitry on high-resistivity float-zone silicon

A new silicon pin-diode-based pixel detector for ionizing particles integrating a two-dimensional array of detecting elements with readout circuitry has been developed and extensively tested. The signal charge is collected on a low-capacitance electrode avoiding loss of charge into the local readout circuitry within each pixel. The spatial resolution for a given circuitry size is optimized. The approach required back side patterning of the wafer, the only nonconventional part in the Stanford BiCMOS based manufacturing process. Thirteen masks on the front side of the wafer and three on the back yielded both CMOS readout circuitry and detecting elements. A gettering step helped obtain a high minority carrier lifetime (500 /spl mu/s). Test results obtained by infrared illumination, gamma rays, and high-energy particles, which have been described in detail elsewhere, are summarized. They include a signal to single-channel-noise performance of about 150 to 1 for a minimum ionizing particle, which is an order of magnitude better than silicon strip detectors currently used, and a record-breaking spatial resolution in the direction of smallest pixel pitch (standard deviation of about 1.8 /spl mu/m). We describe the device and chip operation of the new detector in detail. >