Claude R. Cirba

Physical model for enhanced interface-trap formation at low dose rates

We describe a model for enhanced interface-trap formation at low dose rates due to space-charge effects in the base oxides of bipolar devices. The use of analytical models allows one to reduce significantly the number of free parameters of the theory and to elucidate the main physical mechanisms that are responsible for interface-trap and oxide-trap formation processes. We found that the hole trapping in the oxide cannot be responsible for all the enhanced low-dose-rate sensitivity (ELDRS) effects in SiO/sub 2/, and the contribution of protons is also essential. The dynamics of interface-trap formation are defined by the relation between the proton mobility (transport time of the protons across the oxide) and the time required for positive-charge buildup near the interface due to trapped holes. The analytically estimated and numerically calculated interface-trap densities were found to be in very good agreement with available experimental data.

Total-dose and single-event effects in switching DC/DC power converters

Total-dose and single-event effects in discrete switching DC/DC power converters are examined using a combination of circuit measurements and simulations. The total-dose experiments focus on the response of the power MOSFET used as the switching element for the converters. The efficiencies of two different types of converters (boost and buck) degrade with increasing total dose, leading to eventual functional failure. The single-event transient response of the converters is determined by the response of the feedback control circuitry. Radiation response is studied using both electrical measurements and simulation techniques, and issues affecting circuit failure are identified.

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.

Origins of total-dose response variability in linear bipolar microcircuits

LM111 voltage comparators exhibit a wide range of total-dose-induced degradation. Simulations show this variability may be a natural consequence of the low base doping of the substrate PNP (SPNP) input transistors. Low base doping increases the SPNPs collector to base breakdown voltage, current gain, and sensitivity to small fluctuations in the radiation-induced oxide defect densities. The build-up of oxide trapped charge (N/sub OT/) and interface traps (N/sub IT/) is shown to be a function of pre-irradiation bakes. Experimental data indicate that, despite its structural similarities to the LM111, irradiated input transistors of the LM124 operational amplifier do not exhibit the same sensitivity to variations in pre-irradiation thermal cycles. Further disparities in LM111 and LM124 responses may result from a difference in the oxide defect build-up in the two part types. Variations in processing, packaging, and circuit effects are suggested as potential explanations.

Minimizing gain degradation in lateral PNP bipolar junction transistors using gate control

Gain degradation in lateral PNP bipolar junction transistors is minimized by controlling the potential of a gate terminal deposited above the active base region. Gate biases that deplete the base during radiation exposure establish electric fields in the base oxide that limit the generation of oxide defects. Conversely, gate biases that accumulate the base during device operation suppress gain degradation by decreasing the probability of carrier recombination with interface states. The results presented in this paper suggest that, for gate controlled LPNP transistors designed for operation in radiation environments, a dynamic control of the gate potential improves the transistors radiation hardness and extend its operating life.

Total dose effects on double gate fully depleted SOI MOSFETs

Total ionizing dose effects on fully-depleted (FD) silicon-on-insulator (SOI) transistors are studied when the devices are operated in single gate (SG) and double gate (DG) mode. The devices exhibit superiority in mobility and drain current when operated in DG mode compared to SG mode. Moreover, the dc characteristics of DG operated device are less vulnerable to total dose radiation induced damage. In particular, radiation-induced interface traps have less electrical effect in DG mode operation.

Modeling BJT radiation response with non-uniform energy distributions of interface traps

Radiation-induced oxide defects that degrade electrical characteristics of BJTs can be measured with the use of gated diodes. The buildup of defects and their effect on device radiation response are modeled with computer simulation.

A methodology for identifying laser parameters for equivalent heavy-ion hits

Pulsed lasers show excellent promise for single-event upset (SEU) studies in laboratory environments due to their simplicity of use. However, a one-to-one relationship between a laser hit and a heavy-ion hit has not been developed so far. With the assumption that the collected charge from a SEU hit dictates the circuit-level response, equivalency between a laser hit and heavy-ion hit can be established if the collected charge from both hits is identical. This paper presents a methodology to identify the equivalent laser characteristics for a heavy-ion hit by calculating the collected charge through device-level simulations. Such knowledge will enable SEU hardness assurance of circuits using lasers.

Single event transient effects in a voltage reference

Abstract The Single Event Transient response of the LM236 band gap voltage reference from Texas Instruments is analyzed through heavy ion experiments and simulation. The LM236 circuit calibration was performed using generic transistor parameters that were subsequently optimized using device and circuit simulations. This technique avoids the requirement for performing detailed device-level parameter extraction and simplifies the SET methodology for circuit calibration.

Charge deposition modeling of thermal neutron products in fast submicron MOS devices

Ground-based thermal neutron reaction products (/spl alpha/, /sup 7/Li) appear to be an important terrestrial SEE concern for modern submicron technologies. We address some interesting spatial and temporal characteristics of neutron products. Accurate modeling of the temporal behavior of these products may be required for high-speed devices. In addition, we introduce a simulation methodology that determines device sensitivity to neutron reaction products as a function of neutron nuclear reaction location and the resulting ion track orientation.