Type SOI Research Articles

Minimization of charge sharing effects in a counting type SOI pixel detector for synchrotron radiation

The charge sharing effect among adjacent pixels of a single photon counting detector, which comes from the lateral spread of charges generated from the interaction of X-ray quanta in silicon, has been a critical issue in the pixel detectors due to its influence on the count rate and resolution capability. Targeted on this issue, a single photon counting SOI pixel detector CNPTEG1 used for synchrotron radiation (SR) experiments was developed. It has 17k hexagonal pixels with 52 μm center-to-center pitch while keeping a circuit of charge sharing arbitration logic and 19-bit counter in each pixel. The effectiveness of the charge sharing arbitration logic was verified by using a micro beam with about 10 μm diameter scanning across pixels. The results showed that the count loss or multiple count in pixel boundary was effectively suppressed by the charge sharing arbitration logic with proper threshold setting. The impact of charge sharing on the pixel point spread function (PSF) has also been investigated.

First results of a Double-SOI pixel chip for X-ray imaging

Aiming at low energy X-ray imaging, a prototype chip based on Double-SOI process was designed and tested. The sensor and pixel circuit were characterized. The long lasting crosstalk issue in SOI technology was understood. The operation of pixel was verified with a pulsed infrared laser beam. The depletion of sensor revealed by signal amplitudes is consistent with the one revealed by I–V curve. An s-curve fitting resulted in a sigma of 153 e− among which equivalent noise charge (ENC) contributed 113 e−. It's the first time that the crosstalk issue in SOI technology was solved and a counting type SOI pixel demonstrated the detection of low energy radiation quantitatively.

Design and simulation of blue/violet sensitive photodetectors in silicon-on-insulator

According to Lambert's law, a novel structure of photodetectors, namely photodetectors in silicon-on-insulator, is proposed. By choosing a certain thickness value for the SOI layer, the photodetector can absorb blue/violet light effectively and affect the responsivity of the long wavelength in the visible and near-infrared region, making a blue/violet filter unnecessary. The material of the SOI layer is high-resistivity floating-zone silicon which can cause the neutral N type SOI layer to become fully depleted after doping with a P type impurity. This can improve the collection efficiency of short-wavelength photogenerated carriers. The device structure was optimized through numerical simulation, and the results show that the photodiode is a kind of high performance photodetector in the blue/violet region.

Numerical analysis of alpha-particle-induced soft errors in floating channel type surrounding gate transistor (FC-SGT) DRAM Cell

This paper clarifies alpha-particle-induced soft error mechanisms in floating channel type surrounding gate transistor (FC-SGT) DRAM cells. One FC-SGT DRAM cell consists of an FC-SGT and a three-dimensional (3-D) storage capacitor. The cell itself arranges bit line (BL), storage node and body region in a silicon pillar vertically and achieves cell area of 4F/sup 2/ (F: feature size) per bit. In FC-SGT DRAM cells, the parasitic bipolar current is a major factor to cause soft errors. When an alpha particle penetrates the silicon pillar, generated electrons are collected to the storage node or BL due to the tunneling and diffusion mechanisms. On the other hand, holes are swept into the body region and accumulated. Consequently, the current flows not only in the surface but also in the entire body region due to the floating body effect. This parasitic bipolar current becomes the largest when an alpha particle penetrates the silicon pillar along the vertical axis. However, in case of FC-SGT DRAM cells, the surrounding gate structure can suppress the floating body effect compared with floating channel type SOI DRAM cells. As a result, the loss of the stored charge in the storage capacitor can be drastically decreased by using FC-SGT DRAM cell. Therefore, FC-SGT DRAM is a promising candidate for future high-density DRAMs having high soft-error immunity.

Penetration of solar radiation into the water column of the central subtropical Atlantic Ocean—optical properties and possible biological consequences

The optical properties of the waters as well as the penetration of both solar ultraviolet radiation (UVR) and photosynthetically active radiation (PAR) were analyzed at different stations of the central subtropical Atlantic Ocean during the AZORES II cruise of the research vessel ‘‘Hesperides’’ in April 1999 to assess the impact of solar UVR on microorganisms populating highly transparent oceanic waters. The investigation was based on direct spectral measurements of the scalar and downward-solar irradiance between 290 and 750 nm at different depths using a temperature-stabilized double monochromator spectroradiometer (Optronic, type 754) with a highly sensitive 4p sensor connected to the entrance slit by a 20-m quartz fiber cable. In addition, the Secchi depth was measured, and water samples of different depths at each station were analyzed to determine the concentration and optical properties of phytoplankton as well as attenuating substances such as seston and gelbstoff in the column. Using the spectral irradiance data at different depths as well as the vertical irradiance profiles at different wavelengths, the following parameters were calculated: the spectral attenuation coefficients, the spectral depths of penetration to 1% of the subsurface value (‘‘1% depths’’), the 1% depths for the ranges UV-B, UV-A and PAR, as well as the water type in the Jerlov system of optical classification. The optical properties of the waters investigated can be classified into the oceanic types OI–OII in the Jerlov system, which are characterized by very small concentrations of seston and of gelbstoff, which are the main absorbers for UV radiation in natural waters. The Secchi depths varied between about 15 m (type OII) to about 45 m (type OI) showing ratios to the 1% depths of PAR of about 0.21 to about 0.31. Values of the same order were found for the depths of the maximal concentration of chlorophyll a, which varied between 45 and 100 m during midnight and between 70 and 110 m during noon, showing also significant increases with increasing transparency of the waters. In contrast, the 1% depths for the penetration of solar UV irradiance were found between 12 and 19 m (type OII) and between 26 and 31 m (type OI) for UV-B whereas their values ranged for UV-A between 29 and 65 m (type OII) and between 55 and 93 m (type OI). Thus, solar UV-B penetrates up to about 25% of the photic zone in these waters whereas for UV-A about 75–93% were found. So, solar UVR may significantly affect both the photosynthetic activity by photoinhibition as well as the composition of the kind of species populating different depths of the column by further effects such as DNA damage and inhibition of motility. The role of UVR as a selection factor is shown by a strong absorption peak in the UV range of the water samples, which occurred only when the organisms

Delayed-turn-on phenomenon in accumulation-type SOI pMOS device operating at liquid nitrogen temperature

A unique delayed-turn-on phenomenon in an accumulation type SOI pMOS device operating at 77 K based on the low-temperature PISCES simulation is reported. As compared with the 300 K case, in the delayed-turn-on region, the accumulation-type SOI pMOS device at 77 K may not provide a larger transconductance as a result of the carrier freezeout effects in the thin film.