The oxidation behaviour of metals and alloys at high temperatures in atmospheres containing water vapour: A review

We investigate the breakdown (V/sub br/) enhancement potential of the field plate (FP) technique in the context of AlGaN/GaN power HEMTs. A comprehensive account of the critical geometrical and material variables controlling the field distribution under the FP is provided. A systematic procedure is given for designing a FP device, using two-dimensional (2-D) simulation, to obtain the maximum V/sub br/, with minimum degradation in on-resistance and frequency response. It is found that significantly higher V/sub br/ can be achieved by raising the dielectric constant (/spl epsi//sub i/) of the insulator beneath the FP. Simulation gave the following estimates. The FP can improve the V/sub br/ by a factor of 2.8-5.1, depending on the 2-DEG concentration (n/sub s/) and /spl epsi//sub i/. For n/sub s/=1/spl times/10/sup 13//cm/sup 2/, the V/sub br/ can be raised from 123 V to 630 V, using a 2.2 /spl mu/m FP on a 0.8 /spl mu/m silicon nitride, and 4.7 /spl mu/m gate-drain separation. The methodology of this paper can be extended to the design of FP structures in other lateral FETs, such as MESFETs and LD-MOSFETs.

Enhancement of breakdown voltage in AlGaN/GaN high electron mobility transistors using a field plate

After defining the multiplication factor and the ionization rate together with their interrelationship, multiplication and breakdown models for diodes and MOS transistors are discussed. Different ionization models are compared and test structures are discussed for measuring the multiplication factor accurately enough for reliable extraction of the ionization rates. Multiplication measurements at different temperatures are performed on a bipolar NPN transistor, and yield new electron ionization rates at relatively low electrical fields. An explanation for the spread of the experimental values of the existing data on ionization rate is given. A new implementation method for a local avalanche model into a device simulator is presented. The results are less sensitive to the chosen grid size than the ones obtained from the existing method.

/pdf/impact-ionization-in-silicon-a-review-and-update-2nmz801knv.pdf

Impact ionization in silicon: A review and update

Japanese journal of applied physics : JJAP online.

Over the past four decades, the field of silicon piezoresistive pressure sensors has undergone a major revolution in terms of design methodology and fabrication processes. Cutting edge fabrication technologies have resulted in improved precision in key factors like dimensions of diaphragm and placement of piezoresistors. Considering the unique nature of each sensor and the trade-offs in design, it is not feasible to follow a standard design approach. Thus, it is useful to derive the specific design from a number of important factors to arrive at the `ideal' design. In this paper, we critically review and analyze the various design considerations and principles for silicon piezoresistive pressure sensor. We also report the effect of these considerations on the sensor output taking help of various CAD tools. Keeping in view the accuracy of state-of-the-art fabrication tools and the stringent demands of the present day market, it has become important to include many of these design aspects. Modelling using analytical expressions for thin plates has also been looked into as it gives a quick guideline and estimation of critical parameters before detailed finite element method analysis. Wherever possible, fabrication imperfections and their effects have been discussed. Dependency of piezoresistive coefficients on temperature and doping concentration, the effect of clamping condition of diaphragms and fabrication using wet bulk micromachining is also analyzed. Silicon-on-insulator based sensors along with innovative design strategies, and future trends have also been discussed. This paper will serve as a quick and comprehensive guide for pressure sensor developers.

/pdf/erratum-to-design-principles-and-considerations-for-the-3heux39dno.pdf

Erratum to: Design principles and considerations for the `ideal' silicon piezoresistive pressure sensor: a focused review

Using the recently developed two-dimensional simulator STAAB, the breakdown voltage of the field plate and field-limiting ring junction termination techniques is numerically compared for various values of junction depth, lateral width, and oxide fixed charge. The computed results demonstrate the superiority of the field plate technique over the field-limiting ring technique for planar shallow-junction high-voltage devices, both discrete and integrated. >

Breakdown voltage of field plate and field-limiting ring techniques: numerical comparison

It is shown that normalized breakdown voltages of planar cylindrical junctions are independent of the doping profiles of the junctions and the ionization coefficients used, when the normalization is carried out with respect to plane-parallel breakdown voltage and expressed as a function of normalized radius of curvature rj/Wc, Wc being the depletion layer width on the lightly doped side of the plane-parallel junction at breakdown. It is thus shown that curvature-limited breakdown-voltage calculations can be simplified and that the exact doping profiles and the ionization coefficients need be considered only in the one-dimensional analysis for calculating the plane-parallel breakdown voltage and depletion-layer width on the lightly doped side at breakdown.

On the choice of appropriate ionization coefficients for breakdown voltage calculations

Stiction, or adhesion of components to one another, is a major failure mechanism in surface micromachined MEMS. In this paper we discuss roughening of the surface of polysilicon, which forms the structural layer in surface micromachining, by the formation of porous silicon and its effect on stiction. The adhesivity of the surface is investigated by measurements of contact angle and the roughness is measured by a surface profiler. Measurements to estimate stiction on surface micromachined cantilevers and accelerometers are reported.

Effect of porous silicon formation on stiction in surface micromachined MEMS structures

Treatment of surfaces to change the interaction of fluids with them is a critical step in constructing useful microfluidics devices, especially those used in biological applications. Selective modification of inorganic materials such as Si, SiO2 and Si3N4 is of great interest in research and technology. We evaluated the chemical formation of OTS self-assembled monolayers on silicon substrates with different dielectric materials. Our investigations were focused on surface modification of formerly used common dielectric materials SiO2, Si3N4 and a-poly. The improvement of wetting behaviour and quality of monolayer films were characterized using Atomic force microscope, Scanning electron microscope, Contact angle goniometer, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) monolayer deposited oxide surface.

Self assembled monolayers of octadecyltrichlorosilane for dielectric materials

Analytical expressions for the front and back channel charges and currents in thin-film SOI MOSFETs operating in the subthreshold region are presented, based on a charge sheet model. The analysis includes the charge coupling between the front and back gates and the effect of interface states.

K.N. Bhat

Papers

Breakdown voltage of field plate and field-limiting ring techniques: numerical comparison

On the choice of appropriate ionization coefficients for breakdown voltage calculations

Effect of porous silicon formation on stiction in surface micromachined MEMS structures

Self assembled monolayers of octadecyltrichlorosilane for dielectric materials

Analytical expressions for subthreshold charges and currents in thin-film SOI MOSFETs