H. J. Barnaby

Analysis of single-event transients in analog circuits

A new methodology for understanding single-event transient (SET) phenomena in analog circuits is described. Device and circuit simulation techniques are coupled in order to reproduce experimental data obtained from the National Semiconductor LM124 operational amplifier and to determine the most sensitive parts of the integrated circuit. Experimental data obtained at the Physical Nuclear Institute from a low-power voltage regulator that uses the LM124 are also used to illustrate the method.

Moderated degradation enhancement of lateral pnp transistors due to measurement bias

Enhanced low-dose-rate gain degradation of ADI RF25 lateral pnp transistors is examined as a function of the bias at which the gain is measured. Degradation enhancement at low dose rates diminishes rapidly with increasing measurement bias between the emitter and the base. Device simulations reveal that interface trap charging, field effects from oxide trapped charge and emitter metallization, base series resistance and high-level carrier injection all contribute to this behavior. As a practical consequence, accelerated hardness assurance tests of this device require higher irradiation temperatures or larger design margins for low power applications.

The energy dependence of proton-induced degradation in AlGaN/GaN high electron mobility transistors

The effects of proton irradiation at various energies are reported for AlGaN/GaN high electron mobility transistors (HEMTs). The devices exhibit little degradation when irradiated with 15-, 40-, and 105-MeV protons at fluences up to 10/sup 13/ cm/sup -2/, and the damage completely recovers after annealing at room temperature. For 1.8-MeV proton irradiation, the drain saturation current decreases 10.6% and the maximum transconductance decreases 6.1% at a fluence of 10/sup 12/ cm/sup -2/. The greater degradation measured at the lowest proton energy considered here is caused by the much larger nonionizing energy loss of the 1.8-MeV protons.

Characterization of enhanced low dose rate sensitivity (ELDRS) effects using Gated Lateral PNP transistor structures

The high and low dose rate responses of bipolar transistors in a bipolar linear circuit process technology have been studied with specially designed gated lateral pnp test transistors that allow for the extraction of the oxide trapped charge (N/sub ot/) and interface trap (N/sub it/) densities. The buildup of N/sub ot/ and N/sub it/ with total dose is investigated as a function of the irradiation gate voltage at 39 rad/s and 20 mrad/s for three variations of the final passivation layer (all variations had the same oxide covering the active region of the devices). The three variations in final passivation were selected to exhibit minimal degradation at high and low dose rate (no passivation), significant degradation at high and low dose rate (p-glass/nitride) and enhanced low dose rate sensitivity (ELDRS) (p-glass only). It is shown that the increase in base current is dominated by increased N/sub it/ and the true low dose rate enhancement in the ELDRS parts occurs for zero and negative gate voltage, but is eliminated for large positive gate voltage and elevated temperature irradiation. Implications for ELDRS models are discussed.

Analytical model for proton radiation effects in bipolar devices

The input bias current response of LM124 operational amplifiers to proton irradiation is shown to correlate with the response of identical part types exposed to neutrons and, subsequently, irradiated with X-rays. Moreover, the bias current responses to proton and combined neutron/X-ray exposures are more sublinear than the sum of neutron and X-ray radiation responses measured independently. These data indicate that the ionization defects introduced by proton irradiation moderate the effects of proton-induced displacement damage in the critical bipolar transistors within the LM124. An analytical model is presented that characterizes the various mechanisms of proton radiation effects in bipolar transistors, including the combined effects of oxide charge and bulk traps on carrier recombination. Prototype transistor responses simulated using the model show good correlation with the sublinear characteristics observed in the experimental data. Furthermore, the model is used to assess whether a bipolar junction transistor (BJT), designed with specific structural characteristics and operating in a proton-rich environment, will suffer the most degradation from damage caused by bulk displacement, ionization damage, or a combination of both.

Identification of degradation mechanisms in a bipolar linear voltage comparator through correlation of transistor and circuit response

The input bias current (I/sub IB/) of the National LM111 voltage comparator exhibits a non-monotonic response to total dose irradiations at various dose rates. At low total doses, below 100 krad(SiO/sub 2/), increased I/sub IB/ is due primarily to gain degradation in the circuits input transistors. At high total doses, above 100 krad(SiO/sub 2/), I/sub IB/ shows a downward trend that indicates the influence of compensating circuit mechanisms. Through correlation of transistor and circuit response, the transistors responsible for these compensating mechanisms are identified. Non-input transistors in the circuits input stage lower the emitter-base operating point voltage of the input device. Lower emitter-base voltages reduce the base current supplied by the input transistors, causing a moderate recovery in the circuit response.

Effect of amplifier parameters on single-event transients in an inverting operational amplifier

Laser data and simulation tools are combined to investigate the single-event transient response of the LM124 operational amplifier. The effect of the bandwidth and gain on transients originating in different stages in the operational amplifier is studied. We found that the single-event transient response of the LM124 operational amplifier in an inverting configuration was dependent on the bandwidth of the amplifier, the gain, and on the values of the resistors used to program the gain of the amplifier. We show the results of simulations which illustrate how these changes impact the single-event transient response of the amplifier. An analysis of the results suggests which properties of an operational amplifier will provide a better single-event transient response.

Proton radiation response mechanisms in bipolar analog circuits

The experimental data presented in this paper indicate that the doping and geometry of critical transistors are the primary factors that affect the proton responses of the LM124 and LM148 operational amplifiers. The data also reveal that the electrical responses of these circuits and their input transistors to the combined effects of displacement damage and defects introduced by ionizing radiation are nonlinear. Analysis, supported by device simulation, shows that shifts in device parameters (surface potentials, carrier concentrations, etc.) caused by the buildup of oxide and interfacial defects affect the recombination rate due to traps resulting from displacement damage in the bulk silicon. This nonlinearity complicates the analysis of proton radiation effects and can have a significant impact on the qualification of analog parts for use in space environments.

Investigation of single-event transients in voltage-controlled oscillators

The responses of voltage-controlled oscillators (VCOs) to single-event transients (SETs) are investigated. Laser testing and simulations indicate that ion strikes on critical transistors cause distortions in the oscillating output. The time it takes for the circuit to resume its normal operating condition is limited by the recovery time of the affected transistor(s) and the oscillator startup time. These limits to circuit recovery time are the primary causes of the frequency dependence of SET responses in VCOs.

Separation of ionization and displacement damage using gate-controlled lateral PNP bipolar transistors

Proton irradiation produces both ionization and displacement damage in semiconductor devices. In this paper, a technique for separating the effects of these two types of damage using a lateral PNP bipolar transistor with a gate contact over the active base region is described. By biasing the gate appropriately, the effects of ionization-induced damage are minimized and the effects of displacement damage can be measured independently. Experiments and simulations are used to validate this approach and provide insight into proton-induced BJT degradation.