Preparation of Low-Stress SiN_x Films by Catalytic Chemical Vapor Deposition at Low Temperatures

Abstract

This article covers acoustic design from two main aspects: the design of acoustical devices such as microphones, loudspeakers, etc, and the principles for reduction of sound through partitions, in rooms, etc. These sections are preceded by a description of the behaviour of sound waves and vibrating bodies, and an outline of human response to sound. Finally, special problems in silencing and in the diagnostic use of sound are described. Acoustic design principlesVector velocity of element of source Absorption coefficient of a surface = p / p~, fraction of critical damping Angle of directivity of a dipole source Coefficient of resistive force in a vibrating system Value of p for critical damping of a vibrating system Frequencies of resonance in a rectangular room Density of air Phase lags in vibrating systems Angular frequency. 147 IntroductionThere are two main aspects to acoustical design. The first is concerned with the principles which can be applied to the practical realization of devices such as microphones, loudspeakers, etc, to enable them to work correctly: the second is concerned with the design of devices or structures to reduce noise. Since most problems of noise concern the human subject, the latter aspect of the work necessitates a knowledge of human reaction to noise.This paper deals only with acoustics in the audible region, approximately 20-20000 Hz. Ultrasonics is today virtually a technology on its own. both in communications and in 'sonics'-the term used for the application to engineering devices; while infrasonics (acoustical phenomena below the threshold of hearing) is beginning to develop.The first part of the paper deals with the behaviour of sound waves and the characteristics of random noise. Spectrum measurements and sound-level measurements are described, and human response to noise-ranging from annoyance, through speech interference, to damage to hearing-is outlined.The second part deals with the design of acoustical instruments such as microphones and loudspeakers; this is introduced by a section on the powerful technique of acoustical analogies.The third part deals with design from the point of view of the control of sound waves in auditoria and in transmission through partitions; anti-vibration methods are also described, and the section concludes with a brief review of special methods in silencing and in the diagnostic use of noise. Acoustic sources and fields 2.1. Magnitudes in acousticsOne of the problems in dealing with acoustics is that the physical quantities are so small. The often-quoted statement that the acoustical energy produced by the shouting of a Cup Final crowd would heat enough water to make a cup of tea is accurate enough; even the shouting voice produces an acoustic power of only milliwatts. Of course the aerodynamic energy-to say nothing of other forms of energy-in the process is vastly greater, but conversion efficiencies from aerodynamic to acoustical energy are in the region of 10-4 or 10-5 for many processes.It follows therefore that most acoustical measuremen...

Scanning transmission electron microscope analysis of amorphous-Si insertion layers prepared by catalytic chemical vapor deposition, causing low surface recombination velocities on crystalline silicon wafers

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Hot Wire Chemical Vapor Deposition: Recent Progress, Present State of the Art and Competitive Opportunities

“…SiN x films deposited with conventional methods like PECVD tend to have high stress values in the range of 100-1000 MPa [45]. Passivating layers for organic light emitting diodes for example, require very low stress in the order of 10 MPa [46,47], in addition to low deposition temperatures. Low stress in thin films is also important in micro-electromechanical (MEMS) applications, plastic electronics and when TFTs are deposited on thin polymer foil.…”