PECVD low stress silicon nitride analysis and optimization for the fabrication of CMUT devices

Two technological options to achieve a high deposition rate, low stress plasma-enhanced chemical vapor deposition (PECVD) silicon nitride to be used in capacitive micromachined ultrasonic transducers (CMUT) fabrication are investigated and presented. Both options are developed and implemented on standard production line PECVD equipment in the framework of a CMUT technology transfer from R & D to production. A tradeoff between deposition rate, residual stress and electrical properties is showed. The first option consists in a double layer of silicon nitride with a relatively high deposition rate of ~100 nm min−1 and low compressive residual stress, which is suitable for the fabrication of the thick nitride layer used as a mechanical support of the CMUTs. The second option involves the use of a mixed frequency low-stress silicon nitride with outstanding electrical insulation capability, providing improved mechanical and electrical integrity of the CMUT active layers. The behavior of the nitride is analyzed as a function of deposition parameters and subsequent annealing. The nitride layer characterization is reported in terms of interfaces density influence on residual stress, refractive index, deposition rate, and thickness variation both as deposited and after thermal treatment. A sweet spot for stress stability is identified at an interfaces density of 0.1 nm−1, yielding 87 MPa residual stress after annealing. A complete CMUT device fabrication is reported using the optimized nitrides. The CMUT performance is tested, demonstrating full functionality in ultrasound imaging applications and an overall performance improvement with respect to previous devices fabricated with non-optimized silicon nitride

Numerical Simulation and Experimental Characterization of Emitter Wrap through Solar Cells with Deep Grooved Base Contact (EWT-DGB)

Abstract In this work we present an Emitter Wrap Through cell with Deep Grooved Base contact (EWT-DGB), designed for both 1-sun and concentrating applications. The proposed approach, which consists in a deep grooved hole array composed by holes of two alternating doping type, allows both a reduction of the cell series resistance and an increase in collection efficiency also by using relatively thick substrates with low lifetime. The measured experimental data including dark J-V characteristics, figures of merit (FOMs) under illumination and external quantum efficiency (EQE) are compared to the results of 3-D drift-diffusion TCAD numerical simulations. Moreover, the impact of the hole spacing and of process-dependent physical parameters (interface defects) on FOMs is investigated by means of simulations

Silicon nanocrystals as a photoluminescence down shifter for solar cells

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PixDD: a multi-pixel silicon drift detector for high-throughput spectral-timing studies

The Pixelated silicon Drift Detector (PixDD) is a two-dimensional multi-pixel X-ray sensor based on the technology of Silicon Drift Detectors, designed to solve the dead time and pile-up issues of photon-integrating imaging detectors. Read out by a two-dimensional self-triggering Application-Specific Integrated Circuit named RIGEL, to which the sensor is bump-bonded, it operates in the 0:5 — 15 keV energy range and is designed to achieve single-photon sensitivity and good spectroscopic capabilities even at room temperature or with mild cooling (< 150 eV resolution at 6 keV at 0 °C). The paper reports on the design and performance tests of the 128-pixel prototype of the fully integrated system

The large area detector onboard the eXTP mission

The Large Area Detector (LAD) is the high-throughput, spectral-timing instrument onboard the eXTP mission, a flagship mission of the Chinese Academy of Sciences and the China National Space Administration, with a large European participation coordinated by Italy and Spain. The eXTP mission is currently performing its phase B study, with a target launch at the end-2027. The eXTP scientific payload includes four instruments (SFA, PFA, LAD and WFM) offering unprecedented simultaneous wide-band X-ray timing and polarimetry sensitivity. The LAD instrument is based on the design originally proposed for the LOFT mission. It envisages a deployed 3.2 m2 effective area in the 2-30 keV energy range, achieved through the technology of the large-area Silicon Drift Detectors - offering a spectral resolution of up to 200 eV FWHM at 6 keV - and of capillary plate collimators - limiting the field of view to about 1 degree. In this paper we will provide an overview of the LAD instrument design, its current status of development and anticipated performance

Improvement of Gate Oxide Quality at the Active Region Border

Gate oxide quality at the active border region is known to be quite poor. By adopting a high temperature (1150 °C) dry field oxidation for LOCOS, the gate oxide quality in this border region can be improved to a quality level that is, in terms of charge to breakdown, very close to the characteristics typical for the bulk active region. In this way reliability and yield reduction related to gate oxide failure at the active region border is avoided. A qualitative model is used to support the hypothesi

On the better quality of wet-grown gate oxides

The quality of the gate oxide grown by using both wet and dry oxidation has been studied with respect to the local oxidation atmosphere. Dedicated tests have shown that the difference between wet and dry grown gate oxide is strongly influenced by the previous local oxidation process. A superior quality of wet gate oxide is evident if wet local oxidation has been used, while negligible dependence of gate oxide quality on the gate oxidation ambient is obtained when dry local oxidation is applied

High Electric Field induced positive charges in thin gate oxide

By means of capacitance-voltage technique the positive charging of 9 nm thick silicon dioxide after both positive and negative bias Fowler-Nordheim injection has been evaluated. Measurements results allow to distinguish between two types of positive charge depending on their response to gate voltage variation, i.e. trapped holes and anomalous positive charge. These two types of positive charges also show a different location in the oxide. More precisely, trapped holes are characteristics traps of the SiO2/Si interface and can be found only after negative bias stress, while anomalous positive charges are present in both cathodic and anodic oxide regions independently on the stress polarity

Oxide Growth Effects in Micron and Sub-Micron Field Regions: A Comparison Between Wet and Dry Oxidation

The silicon oxide growth in narrow spacing is affected by the compressive stress present in the oxide and a reduction of the growth rate (field oxide thinning) can occur. In this work it is shown that the stress present in the growing oxide under the oxidation mask induces a field oxide thickening phenomenon which is able to reduce the field oxide thinning one. Furthermore, the comparison between wet and dry oxidation points out the influence of the ammonia in developing the field oxide thinning