Silicon membrane strip photodetectors are fabricated based on thin silicon-on-insulator (SOI) wafers. The thin SOI wafer is realized by exploiting a thinning process on backside. Such detectors can be implemented in proton-beam position detection because its ultra-thin membrane substrate can reduce beam scattering and offer the considerable advantages of higher radiation hardness. A p-spray implantation process is typically performed at the silicon surface between the n+-strips in order to insulate them, without requiring an extra photolithographic mask. In this paper, the sources of leakage current in the detector are first studied by considering both activation energy and simulation analysis in Silvaco TCAD. While the device is operating below avalanche breakdown voltage, the Shockley–Read–Hall process and trap-assisted-tunneling process are dominantly contributing to leakage current. The dominant breakdown voltage is attributed to the premature breakdown in the junction of p−spray/n+ region. The shift of this breakdown voltage under repeated avalanche processes is analyzed in-depth by both experiments and simulations, as a function of temperature and electrical stress conditions, which are introducing an important reliability problem. The electrical stress can be attributed to an increase in fixed charge density at the Si/SiO2 interface. The breakdown voltage finally increases by 4 V after successive avalanche breakdowns as a function of the applied excess bias voltage beyond breakdown voltage.

Ultra-thin silicon-on-insulator-based sensors are presented, featuring a thickness of less than 20 μm, as new integrable items for wearable physical and physiological ultra-low-power applications. Depending on the Si thickness, the back contact realization and the bias conditions, they can be optimized for thermal sensing or optical sensing in the UV-VIS light band. A lateral PIN diode with a transparent graphene back gate shows a maximum responsivity of 0.18 A/W at 390 nm wavelength, and a high sensitivity of ~2.28 mV/°C at fixed 0.01 μA low bias current, whereas a vertical PN strip diode with an Al back contact extends the optical responsivity to the visible range (with e.g. 0.24 A/W at 555nm wavelength when biased at -2 V) and achieves a high-temperature sensitivity using constant reverse voltage method.

In precise hadrontherapy treatments, the particle beam must be monitored in real Lime without being degraded. Silicon strip detectors have been fabricated over an area as large as 4.5 x 4.5 cm(2) with ultra low thickness of 20 mu m. These offer the following considerable advantages: significantly reduced beam scattering, higher radiation hardness which leads to improved detector lifetime, and much better collection efficiency. In a previous work, the novel sensor has been described and a global macroscopic dosimetry characterization has been proposed. This provides practical information for the detector daily use but not about the local microscopic knowledge of the sensor. This work therefore presents a micrometric-accuracy charge-collection characterization of this new generation of ultra-thin silicon strip detectors. This goal is reached thanks to a 1060 nm-wavelength micrometric-sized laser that can be positioned relatively to the sensor with a submicron precision for the three different axes. This study gives a much better knowledge of the inefficient areas of the sensor and allows therefore optimization for future designs. (C) 2013 Elsevier B.V. All rights reserved.

For precise treatment purposes in hadrontherapy, the particle beam has to be monitored in real time without being degraded. For the first time, silicon strip detectors have been fabricated over an area as large as 4.5cm x 4.5cm with ultra low thickness of 20 microns in order to reduce the beam scattering. In this work, we briefly describe the fabrication process and characterize this novel detector consisting of 81 4cm-long strips. Fabrication was carried out in the cleanroom facilities of Université catholique de Louvain starting from p-type thick-SOI wafers. A 62MeV proton beam similar to the ones in clinical treatments has been used to irradiate the sensor at Cyclotron Research Center, Louvain-la-Neuve. The considered parameters were dark current and signal strip repeatability, linearity versus dose rate, and response uniformity through the wafer. The fabrication process was successful and characterization gave satisfactory results. These novel fabricated devices constitute a very promising technology for future in-vivo, non-invasive verification of the actual treatment delivery in hadrontherapy.

In this paper, we present a technology for the fabrication of n-in-p silicon strip detectors, which is based on the use of Al2O3 oxide compared to p-spray insulation scheme. This technology has been developed using the best technological parameters deduced from simulations, particularly for the p-spray implantation parameters. Different wafers were processed towards the fabrication of the radiation detectors with p-spray insulation and Al2O3. The evaluation of the prototype detectors has been carried out by performing the electrical characterization of the devices through the measurement of current-voltage and capacitance-voltage characteristics, as well as the measurement of detection response under radiation. The results of electrical measurements indicate that detectors fabricated with Al2O3 exhibit a dark current several times lower than p-spray detectors and show an excellent electrical insulation between strips with a higher inter-strip resistance. Response of Al2O3 strip detector under radiation has been found better. The resulting improved output signal dynamic range finally makes the use of Al2O3 more attractive.

Hadrontherapy has gained increasing interest for cancer treatment especially within the last decade. System commissioning and quality assurance procedures impose to monitor the particle beam using 2D dose measurements. Nowadays, several monitoring systems exist for hadrontherapy but all show a relatively high influence on the beam properties: indeed, most devices consist of several layers of materials that degrade the beam through scattering and energy losses. For precise treatment purposes, ultra-thin silicon strip detectors are investigated in order to reduce this beam scattering. We assess the beam size increase provoked by the Multiple Coulomb Scattering when passing through Si, to derive a target thickness. Monte-Carlo based simulations show a characteristic scattering opening angle lower than 1mrad for thicknesses below 20 μm. We then evaluated the fabrication process feasibility. We successfully thinned down silicon wafers to thicknesses lower than 10 μm over areas of several cm2. Strip detectors are presently being processed and they will tentatively be thinned down to 20 μm. Moreover, two-dimensional TCAD simulations were carried out to investigate the beam detector performances on p-type Si substrates. Additionally, thick and thin substrates have been compared thanks to electrical simulations. Reducing the pitch between the strips increases breakdown voltage, whereas leakage current is quite insensitive to strips geometrical configuration. The samples are to be characterized as soon as possible in one of the IBA hadrontherapy facilities. For hadrontherapy, this would represent a considerable step forward in terms of treatment precision.