Charles B. Fleddermann

Silicon diodes in avalanche pulse-sharpening applications

Silicon diodes operated in an avalanche breakdown mode can he used to reduce, or sharpen, the rise times of driving pulses. Proper operation of a diode in this manner requires the application of a driving pulse with sufficient time rate of change of voltage dV/dt. The rapidly changing reverse bias produces an electron-hole plasma of sufficient density that the electric field strength in the n region of a p/sup +/-n-n/sup +/ structure is significantly reduced and the plasma is essentially trapped. In effect, the plasma generation causes the device to transition from a high-impedance state to a low-impedance state in a short period of time, and thus acts as a fast closing switch. This paper provides an overview of this mode of operation. A simplified theory of operation is presented. A comparison is made among the results of numerical modeling, the theory of operation of the silicon avalanche shaper (SAS) diode, and the theory of operation of the trapped-plasma avalanche-triggered transit (TRAPATT) mode of operation of a diode. Based on the results of numerical modeling, conclusions are drawn on what factors most greatly affect the performance of avalanche shaper diodes, and one optimized design is provided.

Simple techniques for the generation of high peak power pulses with nanosecond and subnanosecond rise times

A simple method of generating high peak power pulses with nanosecond rise times is described. This method is based on the use of a drift step recovery diode (DSRD) in an inductive‐capacitive storage circuit. A method for sharpening the rise time of the pulses generated using the DSRD to the subnanosecond range is also described. Experimental results show that pulses can be generated with amplitudes of 1.7 kV (into 50 Ω), rise times in the hundreds of picoseconds, and repetition rates of 10 kHz.

Pulse shortening in high-power backward wave oscillators

Pulse shortening is a phenomenon common to all high-power microwave devices. Whereas in electron beam driven sources the electron beam propagation in the device may be for several microseconds or more, the microwave pulse duration is typically no greater than approximately 100 ns. Specific reasons for pulse shortening may vary among devices, but all explanation of the phenomenon put forth involve the introduction of plasma into the interaction region near the walls and/or the degradation of the beam quality. To gain a better understanding of pulse shortening in high power backward wave oscillators (BWOs), an investigation is being conducted at the University of New Mexico (UNM) on the UNM Long-Pulse BWO Experiment. Recent experiments have involved monitoring the beam current in the slow-wave structure (SWS) at different radii as a function of time. The current waveforms are correlated with the time histories of microwave pulses measured in separate experiments. The results reveal the appearance of electrons between SWS ripples at times corresponding to when the microwave signal peaks. A drop in the main beam current is observed shortly thereafter. Coatings of TiO2 and Cr have been placed on the inner surface of the SWS in an effort to suppress electron emission. Initial results with the TiO2 coatings have shown a measurable increase in microwave pulse width.

Plasma etching of PLZT: Review and future prospects

Abstract Future application of ferroelectric thin films in high density integrated electronic and optical circuits will require the development of suitable plasma etching techniques. Although plasma etching is a well developed technology for semiconductors, its application to PLZT thin films is complicated by several factors. In this paper, the prospects for applying plasma etching to PLZT and other perovskite ceramics, will be discussed. This begins with an overview of plasma etching techniques, including a discussion of the applicability of each technique to ceramic thin films. A summary of current plasma etching results for PLZT is presented, which includes a discussion of etch rates, stoichiometry changes, anisotropy, and selectivity that have been observed. Some suggestions for future research required in order for integrated ceramic thin films to be fully realized are presented.

Simulation studies of lateral and opposed contact GaAs photoconductive switch geometry for high power, UWB microwave applications

Summary form only given. The high-gain GaAs Photoconductive semiconductor switch (PCSS) has been studied, using a laser beam as the triggering source. The switch is an integrated component of a parallel plate radiation source, used for driving a TEM horn impulse-radiating antenna. Specifically, the response of a trap filled semiconductor with varying contact placements (lateral and opposed) and material properties have been simulated. The objectives are to identify parameters that would optimize the switch lifetime and hold-off voltage. Beam power and its incidence locations were also varied during the simulation process.

Decomposition of dichloroethane in a plasma arcjet reactor: experiment and modeling

A plasma arcjet reactor has been constructed to study the fundamental reaction kinetics for decomposition of hazardous liquids. The temperature profile of the plasma jet was measured using an enthalpy probe, and the profile was used to model the arcjet as a nonisothermal tubular flow reactor. A surrogate liquid waste-1,2 dichloroethane-was injected into the plasma reactor, and the decomposition byproducts were monitored using a residual gas analyzer. The experimental results were compared to the predicted byproducts from the tubular reactor model and indicated that a photochemical dissociation process accounted for some of the decomposition of dichloroethane. This research also provided a more comprehensive understanding of the critical parameters associated with thermal plasma chemistry and the destruction of liquid waste.

Chapter 7 Critical Technologies for the Micromachining of Silicon

Publisher Summary This chapter discusses critical technologies for the micromachining of silicon. “Micromachining” is a term generally applied to the wide range of three-dimensional (3-D) structures that can be fabricated using techniques originally developed for the microelectronics industry. Principally, micromachining revolves around single-crystal or polycrystalline silicon (Si), although associated materials such as oxides, nitrides, glasses, polymeric materials, and metals are also necessary and used. Other semiconductors such as the III–V compound semiconductors are also the subject of investigations. Various mechanisms for wet-chemical anisotropic etching are discussed in depth in the chapter. This includes several very recent topics, such as innovative electrochemical thinning and porous Si. New data are presented on the chemical formation of micromirrors on Si and GaAs surfaces. The multiple use substrate (MU-STRATE) is discussed in some detail in the chapter as a possible means of reaching into the terabit/cm 3 range of logic element density. A method (signal-induced feedback treatment) of analog e-beam testing and actively modifying up to a billion devices in a few minutes is presented as a way to use the MU-STRATE.

Incorporation of plasma physics and plasma etching into the undergraduate microelectronics laboratory

Experiments encompassing basic plasma physics and etching have been incorporated into the undergraduate microelectronics laboratory at the University of New Mexico. This laboratory is part of a senior level lecture course designed to introduce electrical engineering students to the fundamentals of IC fabrication. A new sequence seeking understanding of the fundamental nature of plasmas used for materials processing is described, together with experiments designed to investigate the effects of plasma reactor parameters on the resulting etch.<<ETX>>