Dale G. Platteter

Mechanisms of Enhanced Radiation-Induced Degradation Due to Excess Molecular Hydrogen in Bipolar Oxides

Bipolar junction test structures packaged in hermetically sealed packages with excess molecular hydrogen (H2) showed enhanced degradation after radiation exposure. Using chemical kinetics, we propose a model that quantitatively establishes the relationship between excess H2 and radiation-induced interface trap formation. Using environments with different molecular hydrogen concentrations, radiation experiments were performed and the experimental data showed excellent agreement with the proposed model. The results, both experimentally and theoretically, showed increased radiation induced degradation with H2 concentration, and device degradation saturate at both high and low ends of H2 concentrations.

Total Dose and Dose Rate Response of an AD590 Temperature Transducer

The total dose response of the Analog Devices AD590 is presented for a variety of irradiation test conditions. The parts packaged in flat-packs show very large enhanced low dose rate sensitive (ELDRS) response for unbiased irradiation, starting at about 20 krad, whereas parts packaged in TO-52 cans are not ELDRS. The reason for this package sensitivity appears to be a result of hydrogen trapped in the cavity of the flat-pack package. The responses at 10 mrad/s and 3 mrad/s are essentially the same, indicating that the low dose rate enhancement factor has leveled off below 10 mrad/s. Elevated temperature irradiation at 100degC and 5 rad/s does not simulate the low dose rate response.

The Effects of Hydrogen in Hermetically Sealed Packages on the Total Dose and Dose Rate Response of Bipolar Linear Circuits

It is demonstrated with test transistors and circuits that a small amount of hydrogen trapped in hermetically sealed packages can significantly degrade the total dose and dose rate response of bipolar linear microelectronics. In addition, we show that when exposed to an atmosphere of 100% molecular hydrogen dies with silicon nitride passivation are unaffected, whereas dies with silicon carbide or deposited oxides become very soft at high and low dose rate.

Enhanced low dose rate sensitivity (ELDRS) in a voltage comparator which only utilizes complementary vertical NPN and PNP transistors

For the first time, enhanced low dose rate sensitivity (ELDRS) is reported in a vertical bipolar process. A radiation hardness assurance (RHA) test method was successfully demonstrated on a linear circuit, the HS139RH quad comparator, and its discrete transistor elements. This circuit only uses vertical NPN and PNP transistors. Radiation tests on the HS139RH were performed at 25/spl deg/C using dose rates of 50 rd(Si)/s, 100 mrd(Si)/s and 10 mrd(Si)/s, and at 100/spl deg/C using a dose rate of 10 rd(Si)/s. Tests at dose rates of 50 rd(Si)/s at 25/spl deg/C and 10 rd(Si)/s at 100/spl deg/C were performed on discrete vertical NPN and PNP transistor elements which comprise the HS139RH. Transistor and circuit responses were evaluated. The dies passivation overcoat layers were varied to examine the effect of removing a nitride layer and thinning a deposited SiO/sub 2/ (silox) layer.

Estimation and verification of radiation induced N/sub ot/ and N/sub it/ energy distribution using combined bipolar and MOS characterization methods in gated bipolar devices

Complementary bipolar and MOS characterization techniques, specifically the gate sweep (GS) and sub-threshold sweep (SS), are used to estimate the radiation induced oxide charge (N/sub ot/) and interface trap (N/sub it/) buildup in gated bipolar test devices. The gate sweep and sub-threshold sweep data from recent TID testing of gated lateral PNP devices suggests an asymmetric energy distribution of interface traps after ionizing radiation exposure. Charge pumping (CP) experiments were done on the test devices to estimate the energy distribution of interface traps induced by radiation. The CP results are used in this paper to confirm the analytical findings from the GS and SS techniques and solidify the use of the complementary method as a simple way of determining radiation induced interface trap distribution in gated bipolar devices.

Wafer Mapping of Total Dose Failure Thresholds in a Bipolar Recessed Field Oxide Technology

Ionizing radiation failure thresholds were measured across a silicon wafer using 10 KeY x-rays to determine the success of hardened process modifications and to examine wafer level hardness assurance screening techniques. Topological wafer maps of the total dose failure response for Signetics 74F00 circuits are presented.

Nature of Interface Defect Buildup in Gated Bipolar Devices Under Low Dose Rate Irradiation

The buildup of radiation-induced switching states in ELDRS-sensitive bipolar base oxides is measured with dc current-voltage and charge pumping techniques. These states include both faster interface traps (Pb) centers) and slower border traps. After irradiation, border traps and interface traps mostly decrease with annealing time and temperature in devices irradiated at 0 V. However, for devices irradiated at -50 V, there is a decrease in border trap density but an increase in interface trap density. These differences in interface-trap buildup and annealing are attributed to the dependence of defect passivation and depassivation on the concentrations of hydrogen and dangling Si bond defects near the Si/SiO2 interface

Assessment of gated sweep technique for total dose and dose rate analysis in bipolar oxides

The efficacy of a gate sweep characterization technique for extracting radiation defect densities in bipolar devices as a function of total dose, dose rate, irradiation bias and device geometry has been studied. The parts analyzed were all NP type gated diodes formed with the n-type emitter and p-type base of a standard linear bipolar process. Diodes, having either 7 or 14 /spl mu/m gate widths, were exposed to ionizing radiation at dose rates of 17 and 0.017 rad(Si)/s with either 0 or 10 V gate biases. Characteristics at several doses were measured using a step stress approach. The majority of the experimental results are shown to be consistent with the space charge model for enhanced-low-dose-rate sensitivity (ELDRS) in bipolar technologies. The results also show, as expected, that gate width has no influence on fixed oxide trapped charge buildup. However, the results suggest the need to refine the standard technique for extracting interface trap densities; where the area of the gate electrode is a critical parameter.

Radiation-induced base current broadening mechanisms in gated bipolar devices

Ionizing radiation experiments on gated lateral bipolar junction transistors (BJTs) show a broadening in the peak base current profile after irradiation. The primary mechanism for this effect is identified as the change in the charge state of interface traps in the oxide over the base. Simulations and theoretical analysis not only describe the mechanism in detail, but also suggest possible solutions for extracting information from the shape of the profile. The effects of the interface-trap energy distribution are investigated, showing that traps between flatband and threshold contribute to the width of the base-current peak.

Modeling Total-Dose Effects for a Low-Dropout Voltage Regulator

Total ionizing dose effects in a low-dropout voltage regulator are explained based on experimental data and circuit simulations. Transistor gain degradation is shown to be the dominant cause of the circuit degradation at lower dose rates. In addition, collector-to-emitter leakage current in one of the NPN transistors of the bandgap reference part of the circuit is responsible for increasing the postirradiation output voltage at high dose rates. Parametric changes in the bandgap, differential amplifier, and output pass transistor circuit blocks are identified that are responsible for various aspects of the observed circuit degradation. The different annealing characteristics of oxide-trap and interface-trap charge are responsible for the complex postirradiation recovery of the output voltage