[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Epitaxial c-axis oriented BiFeO3 (BFO) thin films were deposited on (001) Nb-doped SrTiO3 (Nb-STO) substrates by pulsed laser deposition. Introducing Bi vacancies caused the BFO thin film to evolve to a p-type semiconductor and formed a p-n heterojunction with an n-type semiconductor Nb-STO. The current density versus voltage (J-V) and capacitance versus voltage (C-V) characteristics of the heterojunction were investigated. A typical rectifying J-V effect was observed with a large rectifying ratio of 5×104. Reverse C-V characteristics exhibited a linear 1∕C2 versus V plot, from which a built-in potential of 0.6V was deduced. The results show a potential application of BFO/Nb-STO heterojunction for oxide electronics.

http://absimage.aps.org/image/MAR08/MWS_MAR08-2007-000520.pdf

Rectifying Current-Voltage Characteristics of BiFeO$_{3}$/Nb-doped SrTiO$_{3}$ Heterojunction

The temperature-sensitive electrical parameters (TSEPs) have been used in silicon carbide (SiC) mosfets junction temperature measurement for over-temperature protection and condition monitoring. However, the device aging can affect the TSEPs and thus leads to false ${\boldsymbol{T}}_{\boldsymbol{j}}$ measurement. In this article, the aging's impacts on various TSEPs are comprehensively investigated. Specifically, utilizing the dc power cycling test, both the gate oxide instability and package degradation are considered. Then the commercial devices with different structures are aged, and their temperature-dependent static and switching characteristics are evaluated at different aging cycles. Both the positive gate bias-induced threshold voltage shift and package degradation are observed, and their impacts on each TSEP are evaluated independently. Based on the evaluation results at various operating conditions, the temperature measurement errors due to different aging mechanisms are well summarized for each TSEP. From the dc power cycling test result, the package degradation's impact on TSEPs is found to be more significant than the gate oxide instability. It is pointed out that the aging's effect on TSEPs is an important factor that needs to be considered for accurate ${\boldsymbol{T}}_{\boldsymbol{j}}$ measurement in SiC mosfets .

Evaluation of Aging's Effect on Temperature-Sensitive Electrical Parameters in SiC mosfets

A method for an on-line junction temperature measurement is introduced. The circuit allows the calibration of a real-time thermal model of a power MOSFET. A regular calibration of the real-time model provides an accurate thermal flux model over the lifetime of the power MOSFET. The measurement of threshold voltage is used to determine the device temperature. The paper presents the on-line measurement method, the circuit and test results.

On-line monitoring of the mosfet device junction temperature by computation of the threshold voltage

The research on LED supplementary lighting system for plants

The self-heating effect on the drain current transient response in AlGaN/GaN high electron mobility transistors (HEMTs) was investigated experimentally. Two steps were observed as the drain current dropped with time. The relationship between the transient temperature rise in the channel and the drop in the drain current are discussed in detail. The decrease in the transient drain current and the rise in the channel transient temperature had a complementary relationship. The decrease in the channel electron mobility, caused by self-heating, was an important factor in the drain current drop in the AlGaN/GaN HEMTs.

Effect of Self-Heating on the Drain Current Transient Response in AlGaN/GaN HEMTs

This paper proposes a novel method for junction temperature measurement of power metal-oxide-semiconductor field-effect transistors ( mosfet s). The measurement method is using the turn- on delay of impulse signal, which is the delay time between the rising edge of impulse signal and the corresponding rising edge of drain–source current. Results show that the turn- on delay has a good linear relationship with temperature, and the method is suitably efficient for accurate junction temperature measurement of power mosfet s. The proposed method is verified using the thermal infrared method. Finally, this method is used to measure the real-time junction temperature of power mosfet device in a dc–dc boost converter.

Junction Temperature Measurement Method for Power mosfets Using Turn-On Delay of Impulse Signal

The reliability of GaN high-electron-mobility transistors remains limited by trapping, and a new way to characterize traps is through the drain current transient. In this paper, we report a differential amplitude spectrum (DAS) from which we could extract the exact amount that a trap contributes to charging/discharging from the current transient. We compared the time constant spectrum and the DAS in extracting traps’ amplitudes theoretically and experimentally. Using the DAS, we investigated the trapping effect and systematically identified the positions and mechanisms of traps with ${E}_{a}$ values of 0.10, 0.38, 0.45, and 0.61 eV in our samples. In particular, we demonstrated that the semi-ON state with high-drain voltage in the filling process can maximize the charge trapping in both the AlGaN layer and GaN buffer. In addition, we experimentally proved that measured voltage in the linear region was the best choice for these samples.

Yamin Zhang

Papers

Effect of Self-Heating on the Drain Current Transient Response in AlGaN/GaN HEMTs

Junction Temperature Measurement Method for Power mosfets Using Turn-On Delay of Impulse Signal

A New Differential Amplitude Spectrum for Analyzing the Trapping Effect in GaN HEMTs Based on the Drain Current Transient

Two-dimensional transient simulations of the self-heating effects in GaN-based HEMTs

Identifying the spatial position and properties of traps in GaN HEMTs using current transient spectroscopy