Donald B. King

Damage Equivalence of Heavy Ions in Silicon Bipolar Junction Transistors

Results of displacement damage correlation between neutrons, light ions and heavy ions in bipolar junction transistors are presented. Inverse gain degradation as the function of fluence was measured. The inverse gain degradation due to heavy ion irradiation followed the Messenger-Spratt equation, while some deviation was found for light ions

Metrics for Comparison Between Displacement Damage due to Ion Beam and Neutron Irradiation in Silicon BJTs

We present a series of metrics for comparison between displacement damage due to heavy ion and neutron irradiation in silicon bipolar junction transistors. We have compared ion and fast neutron irradiations to determine an ion-to-neutron damage equivalence. We find that a combination of metrics (damage factor, deep level transient spectroscopy (DLTS) and annealing factor) are needed to ensure a comprehensive understanding of the physics involved in the ion-to-neutron conversion. The linearity of the damage factor (primarily probing the base-emitter junction) is not enough to ensure a valid comparison; rather, we must also use additional techniques (DLTS and capacitance measurements) to ensure that collector compensation is not occurring. As a result, care must be taken in choosing the irradiation beam for ion exposures. The displacement damage should peak in the sensitive region of the device to both ensure maximum gain degradation and to minimize collector compensation.

Simultaneous Evaluation of Neutron Spectra and 1-MeV-Equivalent (Si) Fluences at SPR-III and ACRR

Simultaneous least-squares adjustment of calculated neutron spectra in the central cavity of SPR-III and in the Pb-B4C bucket at ACRR is described, and the resulting 1-MeV-equivalent fluences are compared with damage measurements in 2N2222A transistors.

Comparison Between Experimental and Simulation Results for Ion Beam and Neutron Irradiations in Silicon Bipolar Junction Transistors

We report on an early-time inverse gain comparison between ion and neutron irradiated silicon bipolar junction transistors. We find ion irradiations to be an excellent simulator for fast-burst neutrons for early-time behavior and damage creation rates. In addition we report on an experimental to simulation comparison of transient gain annealing response. The simulations are from a physics based modeling approach that is being developed at Sandia National Laboratories as part of the Qualification Alternatives to the Sandia Pulsed Reactor (QASPR) Program. We find excellent agreement between simulation and experiment across a wide range of irradiation conditions.

Low work function material development for the microminiature thermionic converter.

Thermionic energy conversion in a miniature format shows potential as a viable, high efficiency, micro to macro-scale power source. A microminiature thermionic converter (MTC) with inter-electrode spacings on the order of microns has been prototyped and evaluated at Sandia. The remaining enabling technology is the development of low work function materials and processes that can be integrated into these converters to increase power production at modest temperatures (800 - 1300 K). The electrode materials are not well understood and the electrode thermionic properties are highly sensitive to manufacturing processes. Advanced theoretical, modeling, and fabrication capabilities are required to achieve optimum performance for MTC diodes. This report describes the modeling and fabrication efforts performed to develop micro dispenser cathodes for use in the MTC.

The potential of vacuum microelectronics for space reactor applications

Matrixed field emission devices have been fabricated using a modification of standard integrated circuit fabrication techniques. The emtter‐to‐gate spacing is fixed by the thickness of a deposited oxide and not by photolithograpnic techniques. Functioning triodes have been fabricated using this deposited oxide spacer spproach. Measured emission current to a collector electrically and physically separated from the matrixed emission array follows Fowler‐Nordheim behavior. Modeling of the potential field near the emitter and gate structures as well as the emitted electron trajectories with a two‐dimensional, Poisson solver, finite‐differnce code was used to evaluate and improve field emission structures.

Diamond PCD for Reactor active dosimetry applications

This work reports on the development, calibration, and application of a radiation-hardened diamond photoconducting detector (PCD) for active ionizing dose measurements in research reactors. Results are reported for gamma irradiations between 10 and 10/sup 12/ rad(C)/s.

Application of revised thermionic theory to MTC diodes

An advanced thermionic theory has been developed that focuses on the correct method for incorporating electron reflection when predicting net currents and voltages in vacuum type thermionic diodes. The theory, now complete for vacuum diodes, includes revised equations for predicting net currents, space charge, internal and external electron spectra, and electron cooling. More recently, the theory was extended to include inhomogeneous (patchy) electrode surfaces. The new theory has been used successfully to predict current-voltage curves for Microminiature Thermionic Converter (MTC) diodes. The new theory suggests that the MTC electrodes, at this stage of development, are very patchy and probably exhibit quantum reflection by a dipole on the electrode surface. The excellent agreement of the new theory (and poor agreement of the original theory) with MTC measured performance supports the validity of the revised theory.

Thin Film Dispenser Cathodes for Thermionic Micro-Devices

Electron emissive thin films that possess the thermionic properties of macroscale dispenser cathodes have been fabricated using standard RF sputter deposition techniques. These films are based on a compositionally modulated structure using W and a Ba-containing ternary oxide. These films exhibit uniform work function values of 1.9 to 2.2 eV with high emission coefficients of 2 to 26 A·cm −2 K −2 . Electron microscopy shows that W layer coalescence and continued particle growth occurs with prolonged annealing, eventually disrupting the original surface layer. Chemical modification of the oxide during deposition may provide a route to limit the extent of W coalescence and preserve surface metallization layers on these films. These films are designed to be integrated into thermionic micro-devices.

Results from the microminiature thermionic converter demonstration testing program

Research is in progress to develop microminiature thermionic converters (MTCs) using semiconductor integrated circuit (IC) fabrication methods. The use of IC techniques allows the fabrication of MTCs with an emitter to collector spacing of several microns or less and with emitter and collector materials that will have work functions ranging from 1 eV to 2 eV. Theory predicts that the small emitter to collector spacing and highly emissive low work function electrodes should allow the conversion of heat energy to relatively large electrical current densities (up to tens of Amps/cm/sup 2/) at relatively high conversion efficiencies (15-25%). Tests of prototype MTCs have demonstrated energy conversion at several emitter temperatures. The power generated is less than expected because of less than optimal emission characteristics encountered with the low work function materials used for the first MTC prototypes. Efforts to improve electrode emission characteristics are in progress.