Laleh Najafizadeh

Application of RHBD Techniques to SEU Hardening of Third-Generation SiGe HBT Logic Circuits

Shift registers featuring radiation-hardening-by-design (RHBD) techniques are realized in IBM 8HP SiGe BiCMOS technology. Both circuit and device-level RHBD techniques are employed to improve the overall SEU immunity of the shift registers. Circuit-level RHBD techniques include dual-interleaving and gated-feedback that achieve SEU mitigation through local latch-level redundancy and correction. In addition, register-level RHBD based on triple-module redundancy (TMR) versions of dual-interleaved and gated-feedback cell shift registers is also realized to gauge the performance improvement offered by TMR. At the device-level, RHBD C-B-E SiGe HBTs with single collector and base contacts and significantly smaller deep trench-enclosed area than standard C-B-E-B-C devices with dual collector and base contacts are used to reduce the upset sensitive area. The SEU performance of these shift registers was then tested using heavy ions and standard bit-error testing methods. The results obtained are compared to the unhardened standard shift register designed with CBEBC SiGe HBTs. The RHBD-enhanced shift registers perform significantly better than the unhardened circuit, with the TMR technique proving very effective in achieving significant SEU immunity

Normative database of judgment of complexity task with functional near infrared spectroscopy – Application for TBI

The ability to assess frontal lobe function in a rapid, objective, and standardized way, without the need for expertise in cognitive test administration might be particularly helpful in mild traumatic brain injury (TBI), where objective measures are needed. Functional near infrared spectroscopy (fNIRS) is a reliable technique to noninvasively measure local hemodynamic changes in brain areas near the head surface. In this paper, we are combining fNIRS and frameless stereotaxy which allowed us to co-register the functional images with previously acquired anatomical MRI volumes. In our experiment, the subjects were asked to perform a task, evaluating the complexity of daily life activities, previously shown with fMRI to activate areas of the anterior frontal cortex. We reconstructed averaged oxyhemoglobin and deoxyhemoglobin data from 20 healthy subjects in a spherical coordinate. The spherical coordinate is a natural representation of surface brain activation projection. Our results show surface activation projected from the medial frontopolar cortex which is consistent with previous fMRI results. With this original technique, we will construct a normative database for a simple cognitive test which can be useful in evaluating cognitive disability such as mild traumatic brain injury.

Proton Tolerance of SiGe Precision Voltage References for Extreme Temperature Range Electronics

A comprehensive investigation of the effects of proton irradiation on the performance of SiGe BiCMOS precision voltage references intended for extreme environment operational conditions is presented. The voltage reference circuits were designed in two distinct SiGe BiCMOS technology platforms (first generation (50 GHz) and third generation (200 GHz)) in order to investigate the effect of technology scaling. The circuits were irradiated at both room temperature and at 77 K. Measurement results from the experiments indicate that the proton-induced changes in the SiGe bandgap references are minor, even down to cryogenic temperatures, clearly good news for the potential application of SiGe mixed-signal circuits in emerging extreme environments

SiGe BiCMOS Precision Voltage References for Extreme Temperature Range Electronics

We present the first investigation of the optimal implementation of SiGe BiCMOS precision voltage references for extreme temperature range applications (+120 degC to -180 degC and below). We have developed and fabricated two unique Ge profiles optimized specifically for cryogenic operation, and for the first time compare the impact of Ge profile shape on precision voltage reference performance down to -180 degC. Our best case reference achieves a 28.1 ppm/ degC temperature coefficient over +27 degC to -180 degC, more than adequate for the intended lunar electronics applications

A High-Slew Rate SiGe BiCMOS Operational Amplifier for Operation Down to Deep Cryogenic Temperatures

We investigate, for the first time, the design and implementation of a high-slew rate op-amp in SiGe BiCMOS technology capable of operation across very wide temperature ranges, and down to deep cryogenic temperatures. We achieve the first monolithic op-amp (for any material system) capable of operating reliably down to 4.3 K. Two variants of the SiGe BiCMOS op-amp were implemented using alternative biasing schemes, and the effects of temperature on these biasing schemes, and their impact on the overall op-amp performance, is investigated

On the RF Properties of Weakly Saturated SiGe HBTs and Their Potential Use in Ultralow-Voltage Circuits

We investigate, for the first time, the feasibility of operating silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) in a weakly saturated bias regime to enable ultralow-voltage RF front-end design. Measured dc, ac, and RF characteristics of third-generation high-performance SiGe HBTs operating in weak saturation are presented. Robust RF operation of 0.12 × 6.0 μm2 SiGe HBTs are demonstrated in a common-emitter configuration at collector-to-emitter voltages above 0.15 V. A noise figure of 1.33 dB and an input third-order intercept point above -8 dBm for a 3-GHz input tone are achieved at 0.30 V. These results have potential implications for RF circuits used in severely power-constrained systems.

A Comparison of the Effects of X-Ray and Proton Irradiation on the Performance of SiGe Precision Voltage References

A comprehensive investigation of the performance dependencies of irradiated SiGe precision voltage reference circuits on (1) total ionizing dose (TID), (2) circuit topology, and (3) radiation source is presented. Two different bandgap voltage references were designed using a first-generation (50-GHz) SiGe BiCMOS technology platform, and subsequently exposed to X-rays at doses of 1080 krad(SiO2) and 5400 krad(SiO2). The degradation in circuit performance following X-ray irradiation depends on both the TID level and the chosen circuit topology. Measurement results show that large TID levels can significantly shift the magnitude of the output voltage. Explanations for the observed shifts are provided by utilizing detailed analyses of the two circuit topologies and considering device-to-circuit interactions. The primary factor responsible for the difference in the circuit response before and after irradiation can be attributed to the excess base leakage current in the SiGe HBT. To investigate the impact of radiation source, the circuit topology showing the worst-case degradation from the X-ray experiment was independently exposed to 63-MeV protons at the same effective TID level. A clear source dependence in the circuit response was observed, and possible origins of this behavior are identified.

Accurate Modeling of Single-Event Transients in a SiGe Voltage Reference Circuit

Single-event transients (SETs) are modeled in a SiGe voltage reference using compact model and full 3-D mixed-mode TCAD simulations. The effect of bias dependence and circuit loading on device-level transients is examined with regard to the voltage reference circuit. The circuit SET simulation approaches are benchmarked against measured data to assess their effectiveness in accurate modeling of SET in SiGe analog circuits. The mechanisms driving the SET of this voltage reference are then identified for the first time and traced back to the original device transients. These results enable the differences between the simulation results to be explained, providing new insight into best practices for the modeling circuit SET in different circuit topologies and device technologies.

Quantitative principal component model for skin chromophore mapping using multi-spectral images and spatial priors

We describe a novel reconstruction algorithm based on Principal Component Analysis (PCA) applied to multi-spectral imaging data. Using numerical phantoms, based on a two layered skin model developed previously, we found analytical expressions, which convert qualitative PCA results into quantitative blood volume and oxygenation values, assuming the epidermal thickness to be known. We also evaluate the limits of accuracy of this method when the value of the epidermal thickness is not known. We show that blood volume can reliably be extracted (less than 6% error) even if the assumed thickness deviates 0.04mm from the actual value, whereas the error in blood oxygenation can be as large as 25% for the same deviation in thickness. This PCA based reconstruction was found to extract blood volume and blood oxygenation with less than 8% error, if the underlying structure is known. We then apply the method to in vivo multi-spectral images from a healthy volunteer’s lower forearm, complemented by images of the same area using Optical Coherence Tomography (OCT) for measuring the epidermal thickness. Reconstruction of the imaging results using a two layered analytical skin model was compared to PCA based reconstruction results. A point wise correlation was found, showing the proof of principle of using PCA based reconstruction for blood volume and oxygenation extraction.

Radiation response of SiGe BiCMOS mixed-signal circuits intended for emerging lunar applications

The effects of proton irradiation on the performance of key devices and mixed-signal circuits fabricated in a SiGe BiCMOS IC design platform and intended for emerging lunar missions are presented. High-voltage (HV) transistors, SiGe bandgap reference (BGR) circuits, a general-purpose high input impedance operational amplifier (op amp), and a 12-bit digital-to-analog converter (DAC) are investigated. The circuits were designed and implemented in a first-generation SiGe BiCMOS technology and were irradiated with 63 MeV protons. The degradation due to proton fluence in each device and circuit was found to be minor, suggesting that SiGe HBT BiCMOS technology could be a robust platform for building electronic components intended for operation under extreme environments.