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We report on an research and development activity aimed at the fabrication of silicon microstrip detectors with integrated front-end electronics to be used in high-energy physics and space experiments and medical/industrial imaging applications. A specially tailored fabrication technology has been developed at ITC-IRST (Trento, Italy), which allows for the production of single-sided microstrip detectors, with integrated coupling capacitors and polysilicon resistors, as well as active devices, including N-channel junction field effect transistors and N- or P-channel MOS transistors. The main characteristics of the fabrication process are outlined. Experimental results from the electrical characterization of the devices are reported, showing that transistors with good electrical figures can be obtained within the proposed technology while preserving the basic detector parameters.

We describe our experience on design and fabrication, on high-resistivity silicon substrates, of microstrip detectors and integrated electronics, devoted to high-energy physics experiments and medical/industrial imaging applications. We report on the full program of our collaboration, with particular regards to the tuning of a new fabrication process, allowing for the production of good quality transistors, while keeping under control the basic detector parameters, such as leakage current. Experimental results on JFET and bipolar transistors are presented, and a microstrip detector with an integrated JFET in source–follower configuration is introduced.

A compact, analytical model is derived for the n-side interstrip resistance of double-sided silicon microstrip detectors, allowing for fast and accurate prediction of the minimum p-stop (or p-spray) implant dose ensuring adequate interstrip isolation. The basic idea on which the proposed model relies is that the portion of the detector between two adjacent n-strips can effectively be reduced to an equivalent n-channel MOSFET. The interstrip resistance can be evaluated as the output resistance of this equivalent MOSFET using standard SPICE-like models. The influence of radiation-induced oxide charge and p-stop (or p-spray) voltage can be accounted for by simply including, in the threshold voltage expression, the induced flat-band voltage shift and body-effect term, respectively.

Tetra-methyl ammonium hydroxide, or TMAH, is an anisotropic silicon etchant that is gaining more and more attention in the fabrication process of mechanical microstructures and device isolation, as an alternative to the more usual KOH and EDP etchants [1]: because of its high compatibility with conventional IC processes, due to the absence of metal ions in it. The possibility to passivate the aluminum metalisation in properly saturated TMAH solution has also been demonstrated by doping the solution with appropriate amounts of silicon or silicic acid [2, 3]. This increases the range of application of these etchants, simplifying both the post processing and the etch set-up configuration. In this paper we present some different technological solutions adopted for the fabrication of 3D structures using as anisotropic etchant doped TMAH solutions. The effects of the additives on etch uniformity and surface roughness are studied. Using the etching results under different doping conditions of the TMAH solutions, we obtained silicon bulk-micromachined structures with controlled surface roughness. Furthermore the aluminium passivation permits to etch devices with no protection of the metalisation layers as some applications require (i.e. bolometers).

The low-Q 187Re forbidden beta transition is studied by means of a microbolometers array in order to get a direct limit on the νe mass. The achievable limit of the on-the-shelf small array (ten detectors) in one year measure acquisition time is less than 10eV/c2. Silicon and Germanium thermistors are being developed also for high resolution x-ray spectroscopy; an excellent energy resolution of 5.4eV in the 6keV region has been achieved. This represent the best published result of an Energy Dispersive Sensor (EDS) in this spectral band.

We have fabricated and characterized Si-implanted thermistors to be used as phonon sensors in very-low-temperature, single-quantum detectors. After a short review of the required thermistor properties for this type of application, a detailed description of the production process and of the characterization experimental techniques is reported. The data show that the resistivity-temperature behaviour of all of the devices follows the prediction of the variable range hopping conduction model in the investigated temperature range (4.2-0.03 K). Phonon-electron decoupling and excess low-frequency noise show up at low temperatures, reducing the thermistor sensitivity. These phenomena are discussed and conveniently parametrized in view of a complete detector optimization.

A theoretical study is presented showing that the reverse leakage current thermally generated at the cutting edge of type-inverted p/sup +/-n single-sided silicon microstrip detectors is limited. Such behaviour is shown to be related to a self-limiting mechanism acting on the edge surface generation, which prevents the net generation rate of electron-hole pairs at the detector edge from exceeding a saturation value, as the local hole density approaches its equilibrium value.

Crystals of silver perrhenate were used for the first time in the bolometric measurement of the spectrum of 187 Re with the aim of determining the electron antineutrino mass. The temperature rise was measured by means of neutron transmutation doped germanium and P-implanted silicon thermistors. The energy scale was calibrated using the K lines of Mn and the fluorescence L lines of Sn. Bolometers made from crystals of masses ranging from ∼250 to ∼500 μg were run with FWHM resolutions on the Sn lines ranging from 25 to 60 eV. The end point of the spectrum was located at 2460±5 stat ±10 syst eV. The measured half lifetime was 43±4 stat ±3 syst Gyr, which is in good agreement with the values obtained with mass spectroscopy from the build-up of 187 Os in rhenium samples. The sensitivity of the measurement on a non-zero neutrino mass achievable with these bolometers is discussed.

We show that in high-resistivity silicon bulk generation lifetime and surface generation velocity can not be measured with acceptable accuracy using a single gated diode, unless the gate length is suitably tailored. The accuracy with which bulk generation lifetime can be evaluated is, in particular, limited by nonidealities, contributing extra components to the gated-diode current, which are not accounted for in the standard extraction procedure.

PIN diodes and other test structures have been fabricated on both n- and p-type, high-resistivity, Floating-Zone (FZ) silicon substrates. Different alternative extrinsic-gettering techniques have been adopted to the purpose of meeting the required specification of a detector leakage current density lower than 1 nA/cm2. Phosphorus-doped polysilicon gettering provided the best results on n-type Si with a leakage current density lower than 0.2 nA/cm2 at 100 μm depletion width. On the contrary, devices made on p-type substrates exhibited a leakage current density two orders of magnitude higher. A proper control of the oxide charge at the silicon-silicon dioxide interface was found to be crucial in obtaining a predictable behavior of PIN diode detectors. Some degradation of the reverse leakage current has been observed after device dicing and bonding.

We report on the design of an n-channel Junction Field Effect Transistor (JFET) on fully-depleted, high-resistivity (5 kΩ cm), n-type silicon substrate, which is intended to be utilized as an active device in the on-chip preamplifier of the silicon radiation detectors we are developing. Two-dimensional process and device simulations are employed to optimize the device doping profile, as well as to point out some important advantages of the proposed structure over possible alternative device designs. In particular, the proposed JFET, in which an externally-contacted, p-type well isolates the active device from the high-resistivity substrate, presents higher output-resistance values than a device directly fabricated on substrate. Moreover, it is not affected by a parasitic phenomenon resulting in gate-current increase and noise-performance degradation, which, in contrast, characterizes a device with a floating well.

In current particle physics experiments, silicon strip detectors are widely used as part of the inner tracking layers. A foreseeable large-scale application for such detectors consists of the luminosity upgrade of the Large Hadron Collider (LHC), the super-LHC or sLHC, where silicon detectors with extreme radiation hardness are required. The mission statement of the CERN RD50 Collaboration is the development of radiation-hard semiconductor devices for very high luminosity colliders. As a consequence, the aim of the RandD programme presented in this article is to develop silicon particle detectors able to operate at sLHC conditions. Research has progressed in different areas, such as defect characterisation, defect engineering and full detector systems. Recent results from these areas will be presented. This includes in particular an improved understanding of the macroscopic changes of the effective doping concentration based on identification of the individual microscopic defects, results from irradiation with a mix of different particle types as expected for the sLHC, and the observation of charge multiplication effects in heavily irradiated detectors at very high bias voltages. © 2011 Elsevier B.V.

Silicon bolometers obtained by P implantation on single crystal substrates and compensated with boron in the range 10–50% have been characterized from a technological point of view. Special emphasis was laid on the doping profile of the thermistor, the most critical point of the whole process for an optimal performance of the device as thermal detector. In particular, the effect of post implant anneal on the recovery of the radiation damage and on the modification of the as implanted doping profile is reported. An anomalous enhanced diffusion at 920°C was observed in uncompensated samples. The effect of compensation with B is to reduce the P diffusion, thereby preserving the original as implanted “box” profile almost in haltered. A reproducibility of ±5% of the resistance vs. temperature R(T) characteristic of different bolometers at temperatures below 4.2K has been achieved. This represents an important advancement in the realization of Si bolometers to be used as thermal detectors.

A spectroscopy system, that consists of a 0.8 mm 2 PiN diode coupled to a 100/6 circular N-channel JFET, has been fully tested at room temperature. The energy resolution on the 26.34 keV line is 430 eV FWHM at 3 us shaping time and, at - 5°C, 330 keV at 10 us. The system is ready for the specific applications for which an integrated front-end transistor is needed, but a complete front-end integrated circuit is not viable.

Resistivity measurements carried out in the temperature range 80 mK to 1 K on silicon bolometers-phosphorous doped by ion implantation - at concentrations near the metal-insulator transition, exhibit variable range hopping (VRH) conduction in the whole observed temperature range, with a T-1/2 dependence, in accordance with the Coulomb interaction model for low-temperature conductivity in disordered systems. Samples which apparently show a different behaviour, intermediate between VRH and metallic conduction, can be modelled by a metallic resistance in parallel with an active layer which follows the classic exp(T(O)/T)1/2 law. The observed behaviour can be explained in terms of residual radiation damage induced by the ion implantation process.

In this work we have investigated the feasibility of atmospheric pressure chemical vapor deposition of phosphorus and boron doped silicon oxides from a liquid source—namely TMP (tri-methyl-phosphite)—an alternative to phosphine as a P dopant source'. The most important results on process characterization, dopant incorporation, and film properties are presented. In addition to the easy operation of the liquid source, a remarkable improvement in step coverage has been found, in comparison with PSG deposition from conventional silane and phosphine chemistry.

We report on a new method to measure the electron antineutrino mass, consisting of the end-point study of 187 Re β-spectrum (Q-value=2.6 keV) collected calorimetrically (source=detector approach) with high energy resolution and statistics. The proposed detector is a micro-bolometer, single or in an array structure, containing a total rhenium mass of ∼ 1 mg, operated at a temperature of a few tens of mK and able to reach 10 eV energy resolution. As phonon sensors, we are developing silicon thermistors doped by implantation; some tests are performed also with neutron transmutation doped germanium thermistors. We have obtained up to now promising energy resolutions down to ∼ 11 eV with tin absorbers (as test devices) and ∼ 70 eV with rhenium absorbers.

In this paper we report the development of a prototype for a new kind of detector intended for scintimammography imaging. Traditional photon counting information is available; moreover digital words representing the amplitude of each event and suitable image elaboration methods significantly enhance detector capabilities. The prototype detector is composed of a collimator and 4 imaging modules. Each module is composed of an 8times8 sensing array of 2 mmtimes2 mm silicon p-i-n photodiode pixels, coupled to a CsI(Tl) scintillator and custom readout electronics. The sensor is fixed to an Al2O3 printed circuit board. Eight readout mixed analog-digital ICs, wire bonded to single sensor pixels and to the PCB, provide analog signal conditioning, A/D conversion, self-triggered acquisition and bidirectional serial data transfer. Digital signals are routed out so that each module can be attached to a main board with an FPGA for overall detector management. PC-based supervision of the detector is accomplished using a LabVIEW simplified graphical user interface. The purpose of the prototype is to test the approach and the chosen architecture; all its elements have been designed in order to permit the construction of the final detector with a significantly larger sensing area

"On-chip" electronics fabricated on 6 K/spl Omega/ cm high resistivity wafer is fully characterized and spectroscopic measurements carried out. A new charge sensitive circuit is introduced to amplify the hole signals with on-chip n-channel JFETs and without any resetting devices. The JFET gate-source junction is forward biased and the drain current is stabilized by a low frequency feedback on the JFET p/sup +/ well contact (used as a buried gate for the JFET). Preliminary setups with PIN diodes and tetrode n-JFETs are successfully tested. With about 5 pF total input capacitance, resolution of 86 rms electrons at 223 K with 10 /spl mu/s shaping time is obtained. With about 3 pF, 60 rms electrons at 298 K with 10 /spl mu/s are obtained.

A compact, analytical model is derived for the n-side interstrip resistance of double-sided silicon microstrip detectors, allowing for fast and accurate prediction of the minimum p-stop (or p-spray) implant dose ensuring adequate interstrip isolation. The basic idea on which the proposed model relies is that the portion of the detector between two adjacent n-strips can effectively be assimilated to an equivalent n-channel MOSFET. The interstrip resistance can be evaluated as the output resistance of such an equivalent MOSFET using standard SPICE-like models. The influence of radiation-induced oxide charge and p-stop (or p-spray) voltage can be incorporated into the model by simply including in the threshold voltage expression the induced flat-band voltage shift and body-effect term, respectively.

The accuracy of the gated-diode method for extracting bulk generation lifetime and surface generation velocity in high resistivity silicon is shown to depend critically on the gate length of the adopted test device, as a result of nonidealities which are not accounted for by the measurement technique. Minimization of the surface generation velocity measurement error requires the gate length to be suitably reduced, while long gate devices are needed for accurate bulk generation lifetime extraction. Both parameters can be measured from a single test structure obtained by compenetrating a short gate device with a long gate one.

We report on Junction Field Effect Transistors and PIN diodes monolithically integrated on high-resistivity silicon by adopting a non-standard technology recently developed at IRST. In particular, a test structure, consisting of a small PIN diode DC-coupled to an integrated n-channel JFET in the double-gate configuration was fully characterised and spectroscopic measurements were carried out by adopting a novel double-feedback charge amplifier circuit. An ENC of about 60 electrons r.m.s. has been obtained at room temperature and at 10 μs shaping time; such a resolution is shown to be determined by the relatively high total capacitance present in this preliminary set-up, associated with the 1/ f series noise of the transistor.

We report on the design, implementation and characterisation of a thick-film gas sensor deposited for the first time by screen-printing technique onto a micromachined hotplate, the microheater maintains a film temperature as high as 400°C with 2 was achieved by computer-aided screen-printing. The films were then fired through the microheater itself to guarantee thermodynamic stability for long time exploitation. The response of the device to CO, CH 4 and NO 2 at concentrations typical for indoor and outdoor applications was recorded by measuring the film resistance through ultra high impedance CMOS circuit.

We report on the design, fabrication, and characterization of a microheater module for chemoresistive, metal-oxide semiconductor gas sensors, consisting of a dielectric stacked membrane, micromachined from bulk silicon and with an embedded polysilicon resistor heater. Fabricated structures exhibit excellent heating efficiency, requiring only 30 mW to achieve a temperature of 500 C. Measured electrothermal characteristics are in good agreement with the outcomes of 3D numerical simulations.

This paper is concerned with the preliminary results of a technological study aimed at the development of a fabrication process for double-sided AC-coupled silicon microstrip detectors. The approach adopted for the fabrication of both single-sided and double-sided detectors is presented, and the results from electrical tests performed on detectors and test structures are reported and discussed. Good electrical characteristics as well as an acceptable number of process-related defects have been obtained for these prototype detectors, thus demonstrating the feasibility of fabricating such devices at the IRST facility.

Heavily irradiated p/sup +/-n single-sided microstrip detectors show no dramatic increase in the leakage current due to contributions originating from the cut region, despite, after type inversion, the space-charge region is touching the heavily-damaged, cutting edge, already at zero bias. In this paper, we present both theoretical and experimental results aimed at providing interpretation for such phenomenon. In particular, we show that, for high defect densities at the detector cutting edge, the hole density approaches locally its equilibrium value. Correspondingly, the net generation rate saturates, this ultimately limiting the amount of current which can originate from the detector edge. Measurements from devices irradiated at different fluences are in good agreement with simulation results.

We describe an activity aimed at developing npn silicon bipolar phototransistors to be used in optical position encoders. Extensive numerical proces and device simulations have been carried out, providing the guidelines for the definition of the phototransistor fabrication process. Results from the electrical and optical characterization of manifactured devices are shown. With respect to the designed fabrication process, only a little adjustment of the technological parameters has been to be necessary to achieve a final product suitable for the intended application.

We report on the development of a radiation-detector compatible JFET technology on high-resistivity silicon for monolithic integration of detectors and front-end electronics. A dedicated test-chip has been designed and fabricated for process and device characterization. Results from the electrical characterization of a first fabrication run show that good values of detector leakage current ( ≈1 nA/cm 2 ) can be obtained in spite of the relatively high thermal budget characterizing the process. As far as the JFET performance is concerned, a problem of insufficient device isolation at high substrate voltages has been evidenced. A second run is currently being carried on with the aim of optimizing the JFET structure.

PIN radiation detectors and other test-structures have been fabricated on a FZ, high resistivity (2 k/spl Omega//spl middot/cm), n-type silicon substrate by a process that features three different, alternative extrinsic-gettering techniques. Extremely-low leakage-current values have been measured regardless of the gettering technique adopted, this confirming the effectiveness of gettering procedures in limiting the detector leakage current. In particular, devices exploiting a phosphorus-doped polysilicon backside layer as gettering site have shown the best results in terms of leakage-current and generation-lifetime values. Results from the electrical and optical characterization of such devices are reported and discussed. X-ray detection testing is under way.

We are developing high-resolution Si-implanted thermistors for a calorimetric neutrino mass experiment. The production process is being tuned to reach high performance and reproducibility. We discuss the properties of devices prepared with different process parameters and different geometries. We also present the results obtained using these thermistors for detecting low-energy X-rays.

We are developing Si-implanted thermistors to realize high resolution microcalorimeters. We plan to use these devices in an experiment for the determination of the neutrino mass. The measure implies the evaluation of the correct end-point energy of a beta spectrum with a calorimetric approach. Our study is devoted to outline the optimum fabrication process concerning performances and reproducibility. For such reasons we have realized Si thermistors with different concentration of dopant impurities and with different implant geometries. Tests are performed between 4.2 and 1.2 K using a pumped helium cryostat, and selected samples are characterized at very low temperatures in a dilution refrigerator. Good reproducibility of the devices is necessary for producing an array of detectors. At the same time suitable electronics are developed to optimize the detectors preamplifiers link: minimization of the parasitic capacitance is necessary to reduce the integration of signal and to maximize the speed response of the detector.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Silicate glasses, both undoped and lightly doped with phosphorus, prepared by a low pressure plasma enhanced chemical vapor deposition (PECVD) system using tetraethylorthosilicate or silane as silicon sources and atmospheric pressure chemical vapor deposition technique using silane, were evaluated. The three analyzed phosphosilicate films were nominally 4.0 wt % doped. All the samples were deposited in the temperature range of 350-420-degrees-C. Their main properties such as refractive index, density, wet etch rate, stress, step coverage, moisture resistance, and infrared absorption are reported. Infrared absorption measurements were performed on both as-deposited and annealed films (430-degrees-C for 15 min in N2) to investigate the presence of water and Si-OH groups, as well as P=O and Si-O bond interactions. The P-doped films were tested as final passivation layers on 1 Mbit erasable programmable read only memory devices mounted in ceramic packages. Similar electrical results have been obtained with three different phosphosilicate glass films. However, the most reliable results after assembly and packaging were obtained for films deposited by PECVD technique using tetraethylorthosilicate as the source of silicon in the films

Some insulating films—like SiO2, P-doped SiO2, B-doped SiO2, K-silica glasses, SiaN4, and alumina—are of primary interest in silicon device technology. In this work the main problems concerning the electron and ion beam interactions with these materials when performing Auger analyses are outlined. A few examples of radiation effects are provided. Among these, electron stimulated desorption as well as ion beam induced adsorption and oxide reduction are treated in some detail. General trends in avoiding charging problems with Auger Electron Spectroscopy are provided.

The phosphorus content of P‐doped silicon dioxide films of various compositions was measured with Auger electron spectrometry. Electron and ion beam irradiation were found to severely affect both the energy and the shape of the peak: for very low primary electron current densities a peak, attributed to the phosphorus bonded to oxygen, was found at 110 eV; for higher current densities the 110 eV peak disappeared, and the well‐known peak of elemental phosphorus was found at 120 eV. A reduction effect was also noticed after an ion beam irradiation with 1 keV Ar+ ions: in this case a reconstruction of the broken P‒O bonds was found to take place after irradiation.

A new picture for acceptors in silicon is proposed. Based on the assumption that the hydrogen‐like model holds true irrespective of the value of ionization energy, it implies an effective mass depending on the impurity. This leads to the prediction of new equilibrium and transport properties for moderately doped p‐type silicon.

Variable temperature Hall‐effect measurements on low‐concentration Si:In samples show the existence of supershallow levels with an activation energy for ionization of about 18 meV. For high concentration Si:In samples, the levels at 18 meV tend to disappear and transform into levels with energy of about 160 meV.

The strain entropy of substitutional Group III, IV and V impurities in silicon has been calculated from the experimental solid solubility taking into account the electronic, vibrational and polarization contributions. A correlation between differences of tetrahedral radii and strain entropy is found. Silicon is perhaps the most studied substance after water. In spite of this, there is, at present, no unified description of the solid solubility of impurities in silicon. The usual description correlates the distribution coefficient of an impurity between solid and liquid silicon to its tetrahedral radius. Impurities of the same group lie on the same experimental line (Trumbore 1960). In this work we shall give a correlation between strain entropy and tetrahedral radius that brings together On the same line 10 elements of Groups IIIA, IVA and VA (about 10% of the Periodic Table), and allows the prediction of solid solubility for two other elements.

We show that the accuracy of the gated diode method for measuring bulk generation lifetime and surface generation velocity in high resistivity silicon depends critically on the gate length of the test device, as a result of nonidealities affecting the gated diode operation. Minimization of the surface generation velocity measurement error requires the gate length to be suitably decreased, while long gate length structures are needed for accurate bulk generation lifetime extraction.

We present the developments in a research program aimed at the realization of silicon micro-strip detectors with front-end electronics integrated in a high resistivity substrate to be used in high-energy physics, space and medical/industrial imaging applications. We report on the fabrication process developed at IRST (Trento, Italy), the characterization of the basic wafer parameters and measurements of the relevant working characteristics of the integrated transistors and related test structures.

The experimental work of the Milano group in the search for neutrinoless double beta decay and the direct measurement of the electron antineutrino mass using low temperature detectors is described. Present results on the search for oν-DBD of 130Te and on the preparation of a larger experiment consisting of an array of 20 TeO2 bolometers are discussed. Details about the development of high resolution microcalorimeters for use in a 187Re neutrino mass experiment are given together with the present results obtained in low energy X-ray and β spectroscopy using microcalorimeters both with silicon and NTD thermistors.

We report on an R&D activity aimed at the realisation of silicon microstrip detectors with integrated front-end electronics, to be used in high-energy physics experiments and medical/industrial imaging applications. A dedicated fabrication technology has been developed at ITC-RST (Trento, Italy), which allows for the production of single-sided microstrip detectors, with integrated coupling capacitors and polysilicon resistors, as well as active devices, including N-channel Junction Field Effect Transistors (JFET's), and N- or P-channel MOS transistors. The peculiar characteristics of the fabrication process are outlined, and experimental results from the electrical characterisation of the devices are reported, showing that transistors with good electric figures can be obtained within the proposed technology while preserving the basic detector parameters.

A new test structure intended as a pixel for segmented X- and /spl gamma/-ray detectors has been designed fabricated and tested. The structure consists of a PIN diode of 0.8 mm/sup 2/ area and of an n-channel JFET integrated on the same high resistivity (6 k/spl Omega/ cm) silicon chip. The electrical parameters-leakage current, the transconductance and the capacitance have good expected values. Instead, noise in excess is present in the transistor. Operated at room temperature as an X-ray detector with the integrated frontend transistor in the charge sensitive configuration, the new test structure shows an equivalent noise charge of about 60 electrons rms at the optimum shaping time of 3-6 /spl mu/s.

Anomalies concerning the expected values of resistivity and mobility of indium‐doped silicon in the range where hole scattering is dominated by ionized impurities have been observed. These anomalies can be removed assuming a value of hole effective mass in agreement with the hydrogenlike model of shallow impurities in semiconductors. This suggests a reanalysis of the current picture of hole transport properties in moderately doped semiconductors.

Silicon oxide films formed using two different chemical vapor deposition (CVD) techniques have been characterized by selected etching properties, both in dry (plasma) etching and in wet (chemical) etching. Dry etching was accomplished using CHF3+O2 in a reactive ion etching (RIE) system. The films investigated are undoped silicon oxide, phosphorus‐doped silicon oxide at 4 mol % P2O5, and phosphorus‐doped silicon oxide at 9.5 mol % P2O5. The effects of densification, i.e., thermal treatments carried out at 900 °C in an inert atmosphere (N2) and at 920 °C in steam, are discussed in detail. A decrease in etch rate is observed and considered to be an indication of the structural changes that lead to less porous and more stable films.