Ken K. Chin

Dual-material gate (DMG) field effect transistor

A generic new type of field effect transistor (FET), the dual material gate (DMG) FET, is proposed and demonstrated. The gate of the DMGFET consists of two laterally contacting materials with different work functions. This novel gate structure takes advantage of material work function difference in such a way that the threshold voltage near the source is more positive than that near the drain (for n-channel FET, the opposite for p-channel FET), resulting in a more rapid acceleration of charge carriers in the channel and a screening effect to suppress short-channel effects. Using the heterostructure FET as a vehicle, the principle, computer simulation results, design guidelines, processing, and characterization of the DMGFET are discussed in detail.

Formation of silicon tips with <1 nm radius

Electron emitters in vacuum microelectronic devices need sharp tips in order to permit electron emission at moderate voltages. A method has been found for preparing uniform silicon tips with a radius of curvature less than 1 nm. These tips are formed by oxidation of 5‐μm‐high silicon cones through exploitation of a known oxidation inhibition of silicon at regions of high curvature.

An ultra-sensitive optical MEMS sensor for partial discharge detection

A diaphragm-based interferometric fiber optical microelectromechanical system sensor with high sensitivity is designed and tested for on-line detection of the acoustic waves generated by partial discharges (PD) inside high-voltage power transformers. In principle, the sensor is made according to Fabry Perot interference, which is placed on a micro-machined rectangular silicon membrane as a pressure-sensitive element. A fiber-optic readout scheme has been used to monitor sensor membrane deflection. Sensor design, fabrication, characterization, and application in PD acoustic detection are described. Test results indicate that the fiber optical sensor is capable of detecting PD acoustic signals propagating inside transformer oil with high sensitivity.

Simulation and design of field emitters

Electron emission characteristics for the cone and wedge generic field emitter structures are described. Effects of variations in emitter geometry on electron current, spectral and temporal dispersion of electron emission, and emitter heating are calculated analytically and by computer simulation. Several guidelines for emitter design are suggested. >

Fabry-Perot diaphragm fiber-optic sensor

The general theory of a diaphragm fiber-optic sensor (DFOS) is proposed. We use a critical test to determine if a DFOS is based on Fabry-Perot interference or intensity modulation. By use of the critical test, this is the first design, to the best of our knowledge, of a purely Fabry-Perot DFOS, fabricated with microelectromechanical system technology, and characterized as an audible microphone and ultrasonic hydrophone with orders of improvement in signal-to-noise ratio.

Acousto-optical PD detection for transformers

Partial discharge (PD) is one of the factors that could lead to failure of power transformers, leading to power outage and expensive repairs. The acoustic wave induced by PD can be measured and used for monitoring, diagnosing, and locating potential failures in the transformers. Fiber optic sensors have been shown to be attractive devices for PD detection because of a number of inherent advantages including small size, high sensitivity, electrical nonconductivity, and immunity to electromagnetic interference. A fiber optic sensor based on a Fabry-Perot interferometry is constructed by a simple micromachining process compatible with microelectromechanical system technology. The sensors are used in a transformer to measure PD acoustic waves. The experimental results show the sensor not only has an inherent high signal to noise capability, but is able to accurately localize the PD sources inside the transformer.

The mechanisms of Schottky barrier pinning in III–V semiconductors: Criteria developed from microscopic (atomic level) and macroscopic experiments

Abstract For the sake of perspective, an overview is given of the development of concepts concerning the mechanism involved in Schottky barrier (SB) formation. Until about 1972 principally “macroscopic” data (e.g., I – V and C – V electrical measurements) were available. More recently “atomic” level microscopic tools have been increasingly applied experimentally to the problem of understanding SB formation. The most popular models for the III–V semiconductors are examined in terms of the metal:III–V chemistry including its correlation with barrier height and/or the effect of metal thickness. Experimentally it is found that, for most metals, the Schottky barrier pinning is completed with the deposition of less than a monolayer of metal. Most importantly, the Fermi level pinning position at these low metal coverages is found to correspond well with the SB height obtained from I – V measurements from carefully prepared samples with thicknesses of about 1000 A. On the other hand, the metal:III–V chemistry appears to have little effect on the SB height. For example, four metals - Ag, Au, Cu, and Pd - have very different chemistry (varying from essentially no reaction for Ag to a very strong reaction for Pd); however, they give almost identical SB heights. After comparison of experimental data with various currently popular models, only a refined version of the united defect model is found consistent with the available data.

Annealing of intimate Ag, Al, and Au–GaAs Schottky barriers

Using valence‐band and core‐level photoemission spectroscopy (PES) and electrical device measurements, the effects of annealing Ag, Al, and Au on n‐type (110)GaAs Schottky diodes fabricated in ultrahigh vacuum have been studied. PES was used to monitor the annealing‐induced changes in the interface Fermi level position and the chemical nature of the metal–semiconductor interface for submonolayer and several monolayer coverages. Barrier height determinations were also performed using current–voltage (I–V) and capacitance–voltage (C–V) device measurements on annealed thick metal film metal–semiconductor junctions. The results of this study show that the annealing‐induced microscopic changes in the electronic and chemical structure of the metal–semiconductor interface can be strongly correlated with the macroscopic changes in the electrical properties of thick film metal–semiconductor Schottky diodes.

Atomically sharp silicon and metal field emitters

A method is described for forming atomically sharp silicon tips of less than 10-15 degrees half-angle by utilizing a known oxidation inhibition at regions of high curvature; equally sharp silicon wedges are now made in a similar fashion. The sharp silicon tips serve as the starting point for forming sharp tips of W, beta -W and gold. Field emission data from silicon emitters are compared with Fowler-Nordheim modelling and emission as a function of emitter-anode distance is described. >

Two‐dimensional state of stress in a silicon wafer

Two‐dimensional state of stress in (001) and (111) silicon wafer is studied with infrared photoelasticity. In two widely used groups of coordinate systems, the silicon piezo‐optical coefficient tensors due to photoelastic anisotropy of silicon crystal are derived. The relation between stress ellipsoid and refractive index ellipsoid is analyzed with infrared polarized light transmitting through the silicon crystal in certain directions. The applicability of the stress‐optical law in (001) and (111) silicon wafers is presented. A three direction observation method is developed to decide the magnitude and direction of principal stresses in silicon wafer. The stress states in (100) and (111) silicon wafers after certain device processes are also measured and calculated. Comparisons of experimental and calculated results are made.