Joseph A. Weimer

Dielectric characterization of microwave assisted chemically vapor deposited diamond

Freestanding polycrystalline diamond films produced by Microwave Plasma Chemical Vapor Deposition (MWCVD) were investigated for high power and high temperature electronic applications. The diamond films were deposited on polished tungsten substrates using 5000 W to I500 W power, 15.33 kPa pressure, methane-hydrogen-oxygen precursor gas between 0.5% CH/sub 4/ and 95% CH/sub 4/, oxygen/carbon ratio between 0 and 0.33, and temperature from 600/spl deg/C to 900/spl deg/C. The diamond film parted from the substrate as the samples cooled after deposition due to the difference in the thermal expansion coefficients of diamond and tungsten. Cohesive freestanding films of randomly oriented polycrystalline diamond were obtained ranging from 10 /spl mu/m to 150 /spl mu/m thick Either aluminum or tungsten metal contacts were deposited on the diamond to form parallel plate capacitors. Electrical measurements were performed before and after annealing. The dielectric constant and the loss tangent at temperatures from 23/spl deg/C to 300/spl deg/C were determined from capacitance measurements over a 20 Hz to 1 MHz frequency range. The effect of methane concentration, oxygen concentration, deposition temperature and annealing on the frequency and temperature stability of the dielectric properties of CVD diamond capacitors was investigated. Dielectric constants ranging between 8.0 and 4.2 and resistivities between 1/spl times/10/sup 8/ ohm-cm and 5/spl times/10/sup 14/ ohm-cm were obtained for the diamond samples.

Active Cooling of Metal Oxide Semiconductor Controlled Thyristor Using Venturi Flow

A metal oxide semiconductor controlled thyristor (MCT) is a solid-state high-current switching device. Because of its high-current and high-heat dissipation, this device requires an advanced cooling arrangement. A sample MCT device was successfully tested in a conduction mode up to 95 A using a new technique called venturi cooling. Steady-state operational tests were performed under various coolant temperatures and flow rates. The highest device temperature was 168.5°C, whereas the power dissipation and heat flux were 170 W and 257 W/ cm2, respectively. Comparison with a commercial liquid-cooled cold plate showed that the cooling effectiveness is nearly double for the venturi flow. Measured junction-to-case thermal resistance of the MCT was 0.213°C/ W for venturi flow compared to 0.421°C/W for the commercial cold plate. Venturi flow cooling is highly recommended for MCT applications.

Measured switching speed of MOS‐controlled thyristor under inductive load conditions

The PMOS‐controlled thyristor (PMCT) was tested in a single switch configuration under inductive load conditions. The transient waveforms during turn‐on and turn‐off were observed such as the anode current iA, inductor current iL, anode‐to‐cathode voltage vAK, and gate‐to‐anode voltage vGA. The test circuit was operated for the power levels up to 390 W. These waveforms were obtained for periodic gate drive voltage. The measured turn‐on time was 0.255 μs at 270 V and the measured turn‐off time was 1.6 μs at 16 A. The measured storage time was 1 μs. The measured input capacitance of the MCT was 13.5 nF and the output capacitance was 66.7 nF. It was found that the input and the output capacitances were approximately linear. The turn‐off energy was 2.8 mJ, the turn‐on energy was essentially zero, and the conduction loss was 0.8 W. The MCTs can be used for high power applications.

Implementation of CDFM Generator Control

The control of a cascaded doubly fed machine (CDFM) to be used for aircraft power generation is investigated. The controller employs a resistance simulator in the generator exciter to provide machine damping. Excitation is provided by a six step inverter fed from a controlled rectifier. Delays due to the dc link time constant cause the resistance simulation to be nonideal. An investigation into the ability of resistance simulation to provide damping under these conditions is described. The study includes linearized analysis, simulation, and laboratory tests. Good correlation between these methods was obtained throughout the study. Three control strategies for providing machine damping were investigated, and it is concluded that resistance simulation can be used to provide machine damping under these conditions.

Low temperature processed lead zirconate titanate (PZT) film as dielectric for capacitor applications

Thin PZT film is being developed for use in microelectronics, electromechanical and optoelectronic applications. Thin Pb(ZrTi)O/sub 3/ film capacitor devices were fabricated using RF sputtering techniques. The multiple-layer configuration of Si/SiO/sub 2//Ti/Pt was used as the substrate and bottom electrode. The top electrode was Pt. At 1 kHz, the dissipation factor (tangent loss) of PZT film capacitors processed at 100/spl deg/C was 8.35%. However the dissipation factor of PZT film capacitor processed at 60/spl deg/C was only 0.35%. The dielectric constant was calculated to be 32 at 1 kHz. After annealing at 400/spl deg/C, the dielectric constant increased about 33% to 43. The dielectric constant increased to 165 after annealing at 500/spl deg/C and to 1143 after annealing at 600/spl deg/C. The PZT film capacitors produced to-date had little dependence on frequency from 20 Hz to 100 kHz. The frequency dependence increased with increasing annealing temperature from 400/spl deg/C to 600/spl deg/C. Lowering the processing temperature from 100/spl deg/C to 60/spl deg/C resulted in a tremendous decrease in the dissipation factor from 8.3% to 0.35%.

Multilayer capacitors in polycrystalline diamond by rapid thermal annealing

Polycrystalline diamond (PCD) can be grown over a range of thicknesses from 2 /spl mu/m to over 200 /spl mu/m by a variety of techniques. The PCD films can be obtained with very high resistivities exceeding 10/sup 11/ /spl Omega/-cm or they can be doped with boron to produce high resistance conductors. Metal bonds to polycrystalline diamond (PCD) are important for the realization of ohmic contacts for electronic devices and the adhesion of PCD films to various materials in the fabrication of PCD-based sensors and actuators. We have investigated the formation of titanium contacts on PCD and aluminum silicide bonding of the PCD films to a variety of substrates by rapid thermal techniques. All high temperature process times were kept to 2.5 minutes and only the maximum temperature was varied for optimum results in each sintering step. Two alternative rapid thermal processing systems were used: (a) a cylindrical cavity system with a narrow area coverage for the formation of titanium carbide and titanium silicide bonds, and (b) a rectangular cavity system with large area coverage for the formation of aluminum silicide bonds. The cylindrical cavity system was capable of achieving higher temperatures and was, therefore, used for the formation of the Ti/PCD and Ti/Si contacts. Optimum sintering temperatures were found to be: 885/spl plusmn/15/spl deg/C for Ti/PCD contacts, 710/spl plusmn/5/spl deg/C for Ti/Si and 650/spl deg/C for Al/Si for 36 /spl mu/m thick aluminum foil. Argon gas was used for the ambient in all sintering operations.

A study of MOS-controlled thyristor driver

A prototype of Driver II has been developed by Harris Semiconductor Company. This driver is capable of driving very large capacitive loads, up to 60 nF. It can be used to gate MCTs, IGBTs, and power MOSFETs, both N and P type. The objectives of this paper are to design the external circuit for the MCT Driver II and present experimental test results. The dc power supply voltage was 24 V. The input capacitance of the tested MCT TO/sub 218/ is 18 nF. The output voltage of the driver was varying between -12 V and 12 V. The measured value of the rise was 159.5 ns and the measured value of the fall time was 270 ns.

EXPERIMENTAL STATIC AND DYNAMIC CHARACTERISTICS OF MOS-CONTROLLED THYRISTORS FOR RESISTIVE LOADS

Experimental results are given for a PMOS-controlled thyristor (PMCT). The static IA-VAK characteristics of a PMCT were measured using a programmable high power curve tracer for both forward and reverse anode-to-cathode voltage VAK at different temperatures. The characteristics are similar to the ID-VD characteristics of typical p-n junction diodes. The device has a low forward voltage drop at high-current levels, e.g. VF(AK) = 1.6 V at IA = 200 A. The dynamic behavior of the PMCT was measured in a single switch configuration under resistive loading. The transient waveforms of anode current iA, gate current iG, anode-to-cathode voltage vAK, and gate-to-anode drive voltage vGA were observed at turn-on and turn-off for power levels up to 5 kW. The measured turn-on time was 0.3 μs and the measured turn-off time was 2.2 μs. The switching power loss and the conduction power loss were 3 W and 18 W, respectively.