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Hembree, Charles E.

Publications and source records attributed to Hembree, Charles E..

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Radiation and Self Heating Effects in Hetero-Junction Bipolar Transistors (FY2019 L2 MileStone 6723 Report)

Hetero-Junction Bipolar Transistors (HBT) have several advantages over Silicon Bipolar Junction Transistors (BJT) in radiation environments. One advantage is an intrinsic hardness to displacement damage causing radiation. The generally smaller size of HBTs compared to BJTs also means that less photocurrent is generated by these devices. A disadvantage of the smaller size is less ability to dissipate heat due to smaller surface areas and contacts. This report describes simulations intended to study the initial heating of HBT transistors due to ionizing radiation events and the subsequent heating caused by feedback in the devices when responding to these events.

42 ENGINEERING↗
DOE OSTI2017

Understanding the Implications of a LINAC’s Microstructure on Devices and Photocurrent Models

Here, the effect of a linear accelerator’s (LINAC’s) microstructure (i.e., train of narrow pulses) on devices and the associated transient photocurrent models are investigated. The data indicate that the photocurrent response of Si-based RF bipolar junction transistors and RF p-i-n diodes is considerably higher when taking into account the microstructure effects. Similarly, the response of diamond, SiO 2 , and GaAs photoconductive detectors (standard radiation diagnostics) is higher when taking into account the microstructure. This has obvious hardness assurance implications when assessing the transient response of devices because the measured photocurrent and dose rate levels could be underestimated if microstructure effects are not captured. Indeed, the rate the energy is deposited in a material during the microstructure peaks is much higher than the filtered rate which is traditionally measured. In addition, photocurrent models developed with filtered LINAC data may be inherently inaccurate if a device is able to respond to the microstructure.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

High Accuracy Transistor Compact Model Calibrations

Typically, transistors are modeled by the application of calibrated nominal and range models. These models consists of differing parameter values that describe the location and the upper and lower limits of a distribution of some transistor characteristic such as current capacity. Correspondingly, when using this approach, high degrees of accuracy of the transistor models are not expected since the set of models is a surrogate for a statistical description of the devices. The use of these types of models describes expected performances considering the extremes of process or transistor deviations. In contrast, circuits that have very stringent accuracy requirements require modeling techniques with higher accuracy. Since these accurate models have low error in transistor descriptions, these models can be used to describe part to part variations as well as an accurate description of a single circuit instance. Thus, models that meet these stipulations also enable the calculation of quantification of margins with respect to a functional threshold and uncertainties in these margins. Given this need, new model high accuracy calibration techniques for bipolar junction transistors have been developed and are described in this report.

42 ENGINEERING↗