J.R. Brews

A conceptual model of a single-event gate-rupture in power MOSFETs

Proposes a physical model of hole-collection following a heavy-ion strike to explain the development of oxide fields sufficient to cause single-event gate rupture (SEGR) in power MOSFETs. It is found that the size of the maximum field and the time at which it is attained are strongly affected by the hole mobility. Oxide fields larger than the intrinsic breakdown strength of the oxide can arise from the holes collecting at the interface and their image charge in the gate electrode. These high fields persist for times of the order of picoseconds. It is not known how long these fields must persist to initiate SEGR. >

Impact of oxide thickness on SEGR failure in vertical power MOSFETs; development of a semi-empirical expression

This paper investigates the role that the gate oxide thickness (T/sub ox/) plays on the gate and drain failure threshold voltages required to induce the onset of single-event gate rupture (SEGR). The impact of gate oxide thickness on SEGR is experimentally determined from vertical power metal-oxide semiconductor field-effect transistors (MOSFETs) having identical process and design parameters, except for the gate oxide thickness. Power MOSFETs from five variants were specially fabricated with nominal gate oxide thicknesses of 30, 50, 70, 100, and 150 nm. Devices from each variant were characterized to mono-energetic ion beams of Nickel, Bromine, Iodine, and Gold. Employing different bias conditions, failure thresholds for the onset of SEGR were determined for each oxide thickness. Applying these experimental test results, a previously published empirical expression is extended to include the effects of gate oxide thickness. In addition, observations of ion angle, temperature, cell geometry, channel conductivity, and curvature at high drain voltages are briefly discussed.

Evaluation of SEGR threshold in power MOSFETs

Bias values, determined experimentally to result in single-event gate rupture (SEGR) in power metal oxide semiconductor field effect transistors (MOSFETs), are used in 2-D device simulations, incorporating the experimental geometry. The simulations indicate that very short time oxide field transients occur for ion strikes when V/sub DS//spl ne/OV. These transients can affect SEGR through hole trapping and redistribution in the oxide. >

SEGR and SEB in n-channel power MOSFETs

For particular bias conditions, it is shown that a device can fail due to either single-event gate rupture (SEGR) or to single-event burnout (SEB). The likelihood of triggering SEGR is shown to be dependent on the ion impact position. Hardening techniques are suggested.

Temperature and angular dependence of substrate response in SEGR [power MOSFET]

This work examines the role of the substrate response in determining the temperature and angular dependence of Single-Event Gate Rupture (SEGR) in a power MOSFET. Experimental data indicate that the likelihood of SEGR increases when the temperature of the device is increased or when the incident angle is made closer to normal. In this work, simulations are used to explore this influence of high temperature on SEGR and to support physical explanations for this effect. The reduced hole mobility at high temperature causes the hole concentration at the oxide-silicon interface to be greater, increasing the transient oxide field near the strike position. In addition, numerical calculations show that the transient oxide field decreases as the ions angle of incidence is changed from normal. This decreased field suggests a lowered likelihood for SEGR, in agreement with the experimental trend. >

Domain switching and spatial dependence of permittivity in ferroelectric thin films

A domain model consistent with the measured capacitance–voltage (CV) characteristics of lead zirconate titanate (PZT) capacitors is proposed. Two variants of this model are presented and compared with experimentally measured CV data. The basic model is developed adopting a macroscopic electric field that is spatially uniform through the depth of the film. Then, this model is generalized to allow a variation of the electric field with depth and to include a physically reasonable, position-dependent domain structure. Specifically, the spatial variation of the electric field is related to dopant–ion charges. As a result of the interaction between the domain properties and the electrical doping, a position dependent permittivity is induced, and the electrical properties of the capacitors are affected. Finally, computer simulations to fit the measured CV characteristics are performed to help understand the extent of the coupling between the domain properties and the electrical doping. It is found that there is...

Influence of ion beam energy on SEGR failure thresholds of vertical power MOSFETs

For the first time, experimental observations and numerical simulations show that the impact energy of the test ion influences the single-event gate rupture (SEGR) failure thresholds of vertical power MOSFETs. Current testing methodology may produce false hardness assurance.

Limitations of the uniform effective field approximation due to doping of ferroelectric thin‐film capacitors

The electric‐field distribution in a ferroelectric capacitor often is treated as a uniform effective field for circuit‐level modeling. By solving Poisson’s equation and treating the ferroelectric capacitor as a back‐to‐back Schottky‐barrier system, the nonuniform electric‐field distribution is calculated inside a ferroelectric thin film, assuming that the thin‐film capacitor is completely depleted and has a constant doping concentration. It is found that the departure of the local field from the uniform effective field increases with an increase in the doping concentration of the film. Within this model, the uniform field approach to extraction of microscopic ferroelectric parameters is inaccurate for doping levels great enough that the surface field exceeds the coercive field even at zero bias. Based on this criterion, the critical doping concentration for parameter extraction using the uniform field approximation is found to be about 5×1017 cm−3. That is, according to the assumed model, for the high dop...

PROFILING OF ELECTRICAL DOPING CONCENTRATION IN FERROELECTRICS

In this paper, the extraction of doping profiles in ferroelectric thin-film capacitors using ferroelectric capacitance–voltage (CV) measurements is studied. For a ferroelectric field-dependent permittivity model, the doping profile relation to measured CV curves for ferroelectric thin-film capacitors is found to be analogous to the well-known result of metal–semiconductor Schottky junctions with an easily determined effective dielectric constant. Computer simulation shows the electrical doping concentration of ferroelectric thin-film capacitors can be profiled accurately with the proposed model. Limitations of the model are investigated.

SEGR: a unique failure mode for power mosfets in spacecraft

Power MOSFETs are vulnerable to catastrophic single-event phenomena ena when exposed to the radiation environment of space. In particular, single-event-gate-rupture (SEGR) is a failure mechanism unique to DMOS power transistors caused by the passage of a heavy ion through the neck region of the device and the subsequent transient electric field across the gate oxide. This paper will describe the failure mode, present supporting experimental data, and demonstrate an effective simulation tool for predicting gate rupture.