Characterizing threshold voltage shifts and recovery in Schottky gate and Ohmic gate GaN HEMTs

Threshold voltage shift in normally-OFF GaN High Electron Mobility Transistors (HEMTs) is an important reliability concern in GaN devices. Differences in device architecture between Schottky gate and Ohmic gate normally-OFF GaN HEMTs means that there are important differences in the physical mechanism behind threshold voltage shift due to gate stress. In this paper, a non-intrusive technique for the characterization of threshold voltage shift is applied to both technologies. The technique relies on using a sensing current to measure the third quadrant voltage before and after gate-voltage stress. The results show that in Schottky Gate GaN HEMTs, a positive threshold voltage shift occurs at low gate stress voltages due to electron trapping in the GaN/AlGaN interface while at higher gate stress voltages, the threshold voltage shift becomes negative due to hole trapping and accumulation. The stress time has a fundamental role on the measured threshold voltage shift at medium gate voltage levels and pulsed gate stresses are able to capture this phenomenon. For the Ohmic Gate GaN HEMTs, only a negative threshold voltage shift is observed for all stress currents with no apparent shift as the junction temperature is increased

A c.1244G>A (p.Arg415Gln) mutation in SH3BP2 gene causes cherubism in a Turkish family: report of a family with review of the literature

Objectives: The present study was aimed at advancing the understanding of the pathogenesis of cherubism by presenting a case study based on history, physical examination, typical radiological features, molecular and histo - pathological laboratory tests and a review of the literature. Study Design: This study began with a 7-year-old boy who was referred due to mandibular overgrowth. A pan - oramic radiograph revealed multilocular radiolucent lesions of the upper/lower jaws suggestive of cherubism. Overall, a total of four family members were tested for SH3BP2 mutations, namely two siblings and their parents. Both siblings had been clinically diagnosed with cherubism; however, the parents were clinically normal. Periph - eral blood was collected from all participants and genomic DNA sequencing was carried out. Results: A missense mutation was found in the two affected siblings and their asymptomatic mother. The mu - tation was a 1244 G>A transversion which resulted in an amino acid substitution from arginine to glutamine (p.Arg415Gln) in exon 9. Conclusions: The present study emphasized the importance of further clinical and molecular investigation even when only a single case of cherubism is identified within a family. Genotype-phenotype association studies in individuals with cherubism are necessary to provide important insights into the molecular mechanisms associated with this disease

Impact of threshold voltage shifting on junction temperature sensing in GaN HEMTs

Junction temperature sensing in GaN HEMTs has been identified as a critical challenge for condition monitoring especially under power cycling conditions. The use of temperature sensitive electrical parameters has been widely studied. In GaN devices, the ON-state resistance and gate leakage currents have been identified as TSEPs as both are junction temperature sensitive. Circuits capable of measuring the gate leakage currents in commercially available GaN HEMTs have previously been presented, however, the impact of variability in the threshold voltage on junction temperature sensing requires further investigation. In this paper, junction temperature measurements are implemented using the gate current as a TSEP and are compared with the junction temperature inferred from the ON-state resistance. The measured junction temperatures were verified against electrothermal simulations using manufacturer provided thermal networks. Threshold shift from charge trapping in Schottky GaN HEMTs has been shown to impact the temperature dependence of the gate leakage currents and ON-state resistance. It is important to account for these changes when using them as temperature sensitive electric parameters for real time junction temperature estimation in GaN HEMTs

Isolated Lower Lip Fistulas in Van der Woude Syndrome

Van der Woude syndrome (VWS) is a dominantly inherited disease of orofacial region. Characteristic features of this syndrome are bilateral lower lip sinuses along with cleft lip or palate deformity. However, isolated lower lip pits in VWS without any cleft syndrome is uncommon. Lip pits in VWS are usually asymptomatic; however, patients may complain of watery drainage and/or infection. In this report, asymptomatic isolated lower lip sinuses without any cleft syndrome in a patient and his father are presented