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A Silicon-On-Insulator (SOI) Technology is suitable for vertex detectors for high energy physics experiments since complex functions can be fabricated on the SOI wafer with a small amount of material thanks to the monolithic structure. We developed a new sensor processing scheme “PIXOR(PIXel OR)” for pixel detectors using a LAPIS 0.20 μ m SOI process. An analog signal from each pixelated sensor is divided into two dimensional directions, and 2 n signal channels from a small n by n pixel matrix are ORed as n column and n row channels, then the signals are processed by a readout circuit in each small matrix. This PIXOR scheme reduces the number of readout channels and avoids a deterioration of intrinsic position resolution due to large circuit area, that was a common issue for monolithic detectors. This feature allows high resolution, low occupancy and on-sensor signal processing at the same time. We present the successful results of the PIXOR readout scheme using a first prototype.

We have been developing active pixel sensors based on silicon-on-insulator technology for future X-ray astronomy missions. Recently we fabricated the new prototype named “XRPIX2”, and investigated its spectroscopic performance. For comparison and evaluation of different chip designs, XRPIX2 consists of 3 pixel types: Small Pixel, Large Pixel 1, and Large Pixel 2. In Small Pixel, we found that the gains of the 68% pixels are within 1.4% of the mean value, and the energy resolution is 656 eV (FWHM) for 8 keV X-rays, which is the best spectroscopic performance in our development. The pixel pitch of Large Pixel 1 and Large Pixel 2 is twice as large as that of Small Pixel. Charge sharing events are successfully reduced for Large Pixel 1. Moreover Large Pixel 2 has multiple nodes for charge collection in a pixel. We confirmed that the multi-nodes structure is effective to increase charge collection efficiency.

We have been developing a monolithic active pixel sensor with the silicon-on-insulator (SOI) CMOS technology for use in future X-ray astronomical satellite missions. This sensor is called XRPIX. Our objective is to replace the X-ray CCD, which is currently the standard detector in the field, with the developed XRPIX, which offers high coincidence time resolution (~ 50 ns), superior hit-position readout time (~ 10 μs), and wide bandpass (0.5-40 keV), in addition to having comparable performance in terms of imaging spectroscopy. In our previous study, we built a prototype sensor called XRPIX1 and confirmed its basic X-ray imaging spectroscopy performance in a mode that read out the entire area (all pixels). The next step is to realize a high-speed, intelligent readout for X-ray detection. XRPIX1 comprises a trigger circuit for each pixel, so as to detect an X-ray photon injection; this system is capable of direct access to selected pixels to read out the signal amplitude. We describe the design of the trigger circuitry system and report on the first resolved X-ray spectra obtained in the trigger-driven readout mode.

We have been developing monolithic active pixel sensors with 0.2 μm Silicon-On-Insulator (SOI) CMOS technology, called SOIPIX, for high-speed wide-band X-ray imaging spectroscopy on future astronomical satellites. In this work, we investigate a revised chip (XRPIX1b) for soft X-rays used in frontside illumination. The Al Kα line at 1.5 keV is successfully detected and energy resolution of 188 eV (FWHM) is achieved from a single pixel at this energy. The responsivity is improved to 6 μV/electron and the readout noise is 18 electrons rms. Data from 3 ×3 pixels irradiated with 6.4 keV (Fe Kα) X-rays demonstrates that the circuitry crosstalk between adjacent pixels is less than 0.5%.

We have been developing a monolithic active pixel sensor with the 0.2 μm Silicon-On-Insulator (SOI) CMOS technology, called SOIPIX, for the wide-band X-ray imaging spectroscopy on future astronomical satellites. SOIPIX includes a thin CMOS-readout-array layer and a thick high-resistivity Si-sensor layer stacked vertically on a single chip. This arrangement allows for fast and intelligent readout circuitries on-chip, providing advantages over the charge-coupled device (CCD). We have designed and built a new SOIPIX prototype XRPIX1 for X-ray detection. XRPIX1 implements a correlated double sampling (CDS) readout circuit in each pixel to suppress the reset noise. We obtained an energy resolution of full width at half maximum of 1.2 keV (5.4%) at 22 keV with a chip having a 147 μm sensor depletion at a back bias of 100 V cooled to -50°C. Moreover, XRPIX1 offers intra-pixel hit trigger (timing) and two-dimensional hit-pattern (position) outputs. We also confirmed the trigger capability by irradiating a single pixel with laser light.

In order to investigate the p-side strip isolation, position sensitivity and charge collection of type-inverted double-sided silicon microstrip detectors, signal amplitude and charge sharing of adjacent strips were measured by using a laser test stand, following the irradiation with a flux of 3.8×1013 /cm2 of 12 GeV protons. The irradiated detectors indicated high bulk resistivity, which results in maintaining a position sensitivity of the ohmic contact side even below the full depletion voltage. This fact suggests a possibility of operation of a double-sided detector whose full depletion voltage becomes higher than its breakdown limit because of a radiation damage.

A double-sided, double metal, AC coupled readout silicon microstrip sensor (DDSMS) has been developed for the SVX-II, the upgrade vertex detector for CDF. Key issue in the development is to achieve sufficient radiation hardness for survival in the radiation environment of several kGy/yr. The required high-voltage capability and the reduction of the readout capacitance of the double-metal side were critical design goals. Detailed design methods to radiation-hard silicon sensors are discussed.

A large area (63.6 mm/spl times/64 mm) n-on-n silicon strip detector was fabricated, implementing various p-stop structures in the n-side. The detectors were characterized in laboratory and in beam tests. The inter-strip capacitance showed features in which the individual p-stop structure had the longest tail toward saturation. The beam tests showed other p-stop structures collected more charge in the mid-strip region than the individual p-stop structure. In addition, there was a source which lost or spread charge and induced noise where the over-depletion was insufficient.

We have investigated the micro-discharge (micro-breakdown) phenomenon which is potentially a serious problem in operating in a high radiation environment. Numerical calculation of field strength for the model structure of the microstrip sensor gives us a quantitative understanding of each different cause of micro-discharge. The structure of the microstrip sensor can be optimized through this field calculation for suppressing the micro-discharge. We propose a new strip structure to suppress the micro-discharge.

We have examined experimentally some existing ideas for improving the radiation hardness of silicon microstrip sensors. We confirm that the extended electrode and the deep implant-strip proposed on the basis of simulation studies works effectively to suppress micro-discharge as well as junction breakdown of the bias or guard ring. For an integrated coupling capacitor a double layer structure of SiO 2 and Si 3 N 4 provides better radiation hardness than that of single SiO 2 coupling in our design conditions. The onset voltage of the micro-discharge on the bias/guard ring has been studied for an extended electrode and a floating guard ring.

We report the results of a beam test at KEK using double-sided AC-coupled silicon microstrip detectors with binary readout, i.e., a readout where the signals are discriminated in the front-end electronics and only the hit location as kept. For strip pitch between 50/spl mu/ and 200/spl mu/, we determine the efficiency and the noise background as function of threshold setting. This allows us to reconstruct the Landau pulse height spectrum and determine the signal/noise ratio. In addition, the threshold/noise ratio necessary for operation with low occupancy is determined. >

A full-size prototype microstrip sensor for the silicon tracker of the SDC detector to be used at the Superconducting Super Collider has been fabricated at Hamamatsu Photonics. The sensor is double-sided, using an AC-coupled readout with 50 μm pitch strips. The sensor size is 3.4 × 6.0 cm 2 . Polycrystalline silicon is used as a bias feeding resistor on both surfaces. Each ohmic strip is isolated by a p + blocking line. The detailed requirements for the silicon tracker and the corresponding specifications as well as how to achieve them are discussed. The static performances of this prototype sensor are presented.

Microdischarge at the edges of strips in AC-coupled silicon strip sensors has been investigated. A steep increase in the leakage current (breakdown) and a sudden onset of burst noise were observed at a low reverse-bias voltage when the bias potential was across the AC-coupling capacitor. This can be explained by the occurrence of microdischarges along the edges of strips. These discharges have been confirmed by observing IR light emission. A calculation of the field strength at the strip edge suggests that a fringe field of the external electrode generates the microdischarge at the strip edge when the bias voltage is 50–80 V. This is consistent with our observations. We discuss a design for AC-coupled sensors that eliminates this discharge problem.

To test the radiation tolerance of full-size detectors, four large-area AC-coupled single-sided silicon microstrip detectors were fabricated. The detectors had a size of 6 cm/spl times/3.4 cm and were made out of a 300 /spl mu/m thick, high-resistivity, n-type silicon, simulating the p-side of the double-sided silicon microstrip detectors being developed. The AC coupling layer had either a single layer of SiO/sub 2/ or double layers of SiO/sub 2/ and Si/sub 3/N/sub 4/, in combination with the surface passivation of SiO/sub 2/ or Si/sub 3/N/sub 4/. The detectors were irradiated at room temperature by 500 MeV protons at TRIUMF to a fluence of 5.7/spl times/10/sup 13/ protons/cm/sup 2/, promptly stored at 0/spl deg/C after irradiation, and periodically measured over the following year. The full depletion voltages showed a substantial annealing and a gradual anti-annealing. The result was compared with the predictions of existing damage parameterization. Time variation of other characteristics, such as leakage current, interstrip and coupling capacitances, and strip-edge microdischarges was also followed. >

A double-sided silicon strip detector with a radiation-tolerant design was fabricated and characterized in a sequence of beam tests at KEK using 4 GeV/ c pions. The detectors were combined with newly designed, fast, lower power, bipolar amplifier-shaper-discriminator chips and CMOS digital pipeline chips to record hit-no hit signals in the strips. Efficiencies, noise occupancies, and spatial resolutions were measured before and after the proton irradiation at an equivalent fluence of 1 × 10 14 p/cm 2 , depending on angle of track incidence and strip-pitches. The median pulse height distribution, derived from the threshold scans of the efficiency, allowed to extract the response of the detector. A 1 T magnetic field enabled us to determine the Hall mobilities of electrons and holes.

Precision tracking and vertex reconstruction play a crucial role in heavy flavor physics at CDF, in reconstructing the charm and beauty decay vertices in beauty and top events. A significant upgrade to the CDF detector, including a new silicon tracker, will support an extensive physics program with the high luminosity provided by the Main Injector accelerator upgrade. The specifications and design considerations for this new silicon tracker/vertex detector are discussed.