C. Rente

Radiation and cryogenic test results with a monolithic GaAs preamplifier in C-HFET technology

Abstract We report test results with a monolithic GaAs preamplifier fabricated in industrial C-HFET technology irradiated with a total dose of 10 14 neutrons/cm 2 and 100 Mrad γ radiation and operated under cryogenic conditions. The measured gate current of the input transistor of a few nA increases by

Development of a bump bonding interconnect technology for GaAs pixel detectors

Abstract Pixel detectors made of semi-insulating GaAs have already been successfully tested for their application as tracking detectors in high energy physics experiments. For the operation of large arrays of pixel sensors, a technology allowing a two dimensional interconnect with a high yield is necessary. For this purpose an indium based bump bonding process has been developed. Especially the generation of the indium bumps on the surface of the GaAs pixel detector was optimized. The development of these processing steps is described. In order to investigate the influence of these steps and of the bonding procedure on the detector performance, I – V -characteristics of bump bonded GaAs pixel detectors were analyzed.

Investigation of the radiation damage of GaAs detectors by protons, pions and neutrons☆

Abstract Surface barrier detectors processed in Aachen using SI-GaAs from several manufacturers have been irradiated with high fluences of neutrons (mean energy 1 MeV, fluence up to Φ n ∼ 5 × 10 14 cm −2 ), pions (191 MeV, fluence up to Φ π ∼ 0.6 × 10 14 cm −2 ) and protons (23 GeV, fluence up to Φ p ∼ 2 × 10 14 cm −2 ). The detectors have been characterized in terms of macroscopic quantities like I - V characteristic curves and charge collection efficiencies for incident minimum ionizing- (mip) as well as α-particles. All detectors work well after the exposure. At the highest fluences a sizable degradation concerning the charge collection efficiencies has been observed for all investigated materials. SI-GaAs material with low carbon content (LC material from FCM, Freiberg) seems to be less affected than substrates with a higher carbon concentration. At the highest irradiation level the mip signal from a 250 μm thick detector made of LC material amounts to 8000 electrons (at 400 V bias voltage) independent of peaking times between 40 ns and 2.2 μs. The leakage currents for this material are even reduced after the irradiation.

Investigation of a bump bonding interconnect technology for GaAs pixel detectors

Abstract Pixel detectors made of semi-insulating GaAs have already been successfully tested for their application as tracking detectors in high energy physics experiments. For the operation of large arrays of pixel sensors, a technology allowing a two-dimensional interconnect with a high yield is necessary. For this purpose a bump bonding process was developed. In this paper the, yield and the resistance of the interconnections is analyzed. With more than 2700 interconnections on special test structures the resistance of a single bump-bond is consistent with zero Ohm and the yield was determined to be 92%.

Radiation hardness of MSM biasing structures for GaAs microstrip detectors

Abstract In order to achieve a high signal-to-noise ratio and a low-space consumption it is necessary to use integrated resistors for the biasing of GaAs microstrip detectors used in high-energy physics experiments (e.g. CMS, H1). Metal-semiconductor-metal (MSM) structures operating in the reach through regime seem to be a promising solution for that purpose. According to the requirements on radiation hardness of strip detectors to be used in the CMS experiment, we have irradiated MSM biasing structures with up to 4.6 × 10 14 neutrons cm 2 . The radiation effects on the dc and noise characteristics of the devices are investigated. Furthermore, the effects of an annealing procedure are examined.

Measurements on GaAs strip and pixel detectors in a 50 GeV pion beam

Abstract GaAs strip and pixel detectors constructed in Aachen have been tested at CERN in a 50 GeV pion beam in September 1995 in collaboration with the CMS Tracker group. The strip detectors had a pitch of 100 μm and were made of a 250 μm thick Freiberger SI-GaAs wafer [1]. The three strip detectors had a strip width of 25, 50 and 75 μm, respectively. Using the fast PreMux128 preamplifier multiplexer chip ( τ p = 50 ns) a signal to noise ratio of 15 was obtained for the widest strips at normal beam incidence for a bias voltage of 170V. The 8 × 8 pixel arrays with a pixel size of 1 × 1 mm 2 and 0.5 × 0.5 mm 2 , respectively, were read out with the PreMux128 as well. Here a signal of 12500e − was obtained for both detectors, leading to a maximum signal to noise ratio of 20 at perpendicular beam incidence and 170 V bias voltage.

Beam test measurements on GaAs pixel detectors at various angles of incidence

Abstract A GaAs pixel detector constructed in Aachen has been tested in a 4 GeV electron beam at DESY. The experimental setup allowed tilting the detector with respect to the beam line with angles of incidence from 0° to 45°. The sensor-array consisted of 8 × 16 pixels with a size of 125 × 125 μm2 each. The detector was made of a 250μm thick Freiberger SI-GaAs wafer. An improved contact was formed on the backside, allowing safe operation of the detector in the soft breakdown regime. A double metal technique allowed bonding the single pixels linearly to the readout-chip. Using the the fast PreMux128 preamplifier multiplexer chip (τp = 40ns) a signal to noise ratio of 29 was obtained for a beam angle of incidence of 0° increasing up to 38 for 45°. The spatial resolution obtained with an angle of incidence of 45° was (9.0 ± 6.0) μm while the resolution of the untilted detector is equal to the digital one (36.1μm). For these testbeam-measurements the detector was connected to the electronics via wire-bonds. For future experiments bump-bonding connections are required. The results of a process for the formation of bump-bond connections on GaAs pixeldetectors are shown.

Beam test measurements on GaAs strip and pixel detectors

Abstract GaAs strip and pixel detectors constructed in Aachen have been tested in a 1.4 GeV electron beam in Bonn and in a 5 GeV electron beam at DESY in February and May 1997. The strip detectors had a pitch of 50μm with a strip width of 25μm and were made of a 250μm thick Freiberger SI-GaAs wafer. The strip detectors included a punch-through bias structure and an integrated coupling capacitor. Additionally, an improved backside contact was formed, allowing a safe operation of the detector in a soft breakdown regime. Using the fast PreMux 128 preamplifier multiplexer chip ( τ p = 50 ns) a signal-to-noise ratio of 13 was obtained at normal beam incidence for a bias voltage of 200 V, leading to a spatial resolution of 11 μm with a simple COG algorithm. The 8 × 16 pixel array with a pixel size of 125 × 125 μ m 2 was read out with the PreMux128 as well. With a double-metal technique, it was possible to bond the single-pixels linearly to the amplifier chip. The obtained signal-to-noise ratio of 30 in combination with a COG algorithm lead to the digital resolution value of 36 μm for both pixel coordinates.

Radiation hardness of GaAs complementary heterojunction field effect transistors (CHFETs) and CHFET-based monolithic amplifiers☆

We report measurement results with single GaAs complementary heterojunction field effect transistors (CHFETs) and monolithic CHFET-based operational amplifiers. The devices have been exposed to neutrons (1 MeV peak energy, total fluence of 5 × 1014ncm2) and protons (23 GeV, total fluence of 5 × 1014pcm2). The amplifiers irradiated with 5 × 1014neutronscm2 had already been irradiated either with photons from a 60Co source for a 100 Mrad dose or with 1014neutrons/cm2. All devices remained fully functional after irradiation. We compare their amplification and noise parameters before and after the (additional) exposure.

Measurements on a GaAs microstrip detector with 50 GeV/c electrons☆

Abstract A microstrip gallium arsenide detector (thickness 508 μm, strip width 100 μm, strip pitch and readout pitch 200 μm) has been tested in a 50 GeV/ c electron beam at CERN. Using the low noise Viking preamplifier chip (shaping time ∼1.5 μs) signal to noise ratios up to 25 were measured depending on bias voltage and angle of incidence. Applying the so-called η-algorithm (using the impact position-sensitive charge sharing between adjacent strips) a resolution down to σ ∼ 20 μ m could be obtained.