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Lithology identification is the research basis in oil and gas reservoir exploration and is critical for the formation characterization and reservoir development. Traditional lithofacies identification methods rely on the knowledge and experience of geologists and are usually done manually. With the development of deep learning technology and its application in the field of geophysics, lithofacies identification based on deep-learning approach has attracted great attention in recent years. Well logging data have obvious sequence characteristics. Therefore, we propose to use a bidirectional long and short-term memory (BiLSTM) neural network to learn long-term information for more effective lithology facies classification. In addition, we also perform correlation analysis on the input well logging curves and conduct median filter at different scales according to the correlation degree to extract the geological features within data itself and discard the interference of noise. The raw data-based lithofacies identification can reflect the noise resistance of the neural network model to some extent, while the filtered data are more beneficial for the model to extract the geological features correlated with lithofacies and provide accurate classification results. We validate our proposed framework by applying it to a case study from the Council Grove gas reservoir located in Kansas. Furthermore, we compare the effect of input data and network model on the identification results. The experimental results show that the proposed lithofacies identification method has higher classification accuracy. [ABSTRACT FROM AUTHOR]

Excellent high-temperature performance (298–523 K) of the 4H-SiC n-p-n bipolar phototransistor detector (PTD) was explored. It was fabricated using the 4H-SiC epitaxial wafer grown by high-temperature chemical vapor deposition (HTCVD). The static and dynamic properties of the device were tested and analyzed. The results show that the device still has an optical gain of up to 103, a wide linear response range, and good repeatability at the high temperatures up to 523 K under a 3-V bias with a wavelength of 360 nm. The temperature coefficient of the optical gain is extracted, the value of which is 1.02/K. Although the response time of the device increases with the temperature, the increased percentage in responsivity is significantly greater than that of the response time. The results provide an important experimental reference for the application of high-temperature detection and suggest that the PTD has the potential to be used in ultraviolet (UV) detecting systems at high temperatures. [ABSTRACT FROM AUTHOR]

In this article, we report the first experimental results of a novel 4H-silicon carbide (SiC) p-i-n photodetector based on a vertical nanocone array (NCA). It is fabricated by electron beam lithography and inductively coupled plasma (ICP) etching technology. The performance of static and dynamic behavior was studied systematically. It shows the responsivity of ~41.9 mA/W under 360 nm at a bias voltage of −0.5 V and has a linear response to the ultraviolet (UV) light in a wide light intensity range of 0.1–104 mW/cm2. The response time decreased as the light intensity rose from 3 mW/cm2 to 5 W/cm2 and then leveled off at higher light intensity (>100 mW/cm2), which is about 0.25 ms. The photodetector −3-dB cutoff is ~3400 Hz at $\boldsymbol {\lambda } = 360$ nm and light intensity = 100 mW/cm2. Besides, the detector can respond to the UV light from 260 to 360 nm and the peak responsivity is ~78 mA/W at 320 nm. The analysis results have reference values for the development of an innovative 4H-SiC UV photodetector to some extent. [ABSTRACT FROM AUTHOR]

A two-terminal 4H-SiC n-p-n bipolar phototransistor detector (PTD) with high gain is demonstrated. It was fabricated using the 4H-SiC epitaxial wafer grown by high-temperature chemical vapor deposition. The PTD shows a large photocurrent and responsivity enhancement over the conventional 4H-SiC p-i-n photodetector (PD). These enhancement effects are owing to the internal gain of the bipolar transistor. The detector shows a high optical gain of ~ 1450 at 360 nm and has a linear response to the ultraviolet (UV) light in the wide light intensity range of 0.7– 700 μW/cm2 at a low operating voltage of 3 V. The PTD can respond to the UV light from 220 to 340 nm and the peak responsivity is ~ 125A/W at 275 nm. This work is significant for developing high-performance SiC-based bipolar phototransistors. [ABSTRACT FROM AUTHOR]

Considering potential applications related to superconductivity and aerospace (typically less than 100 K), in this article, the temperature dependence of silicon carbide (SiC) power diodes is systematically characterized and analyzed over a wide temperature range of 90–478 K, especially focusing on cryogenic temperature. First, the static performance degradation mechanism of SiC diodes is established in an ultrawide temperature range, including forward/reverse I-V characteristics and junction capacitance (Cj) characteristics. Second, the reverse recovery characteristics are achieved, including peak reverse recovery current (Irm), reverse recovery charge (Qrr), and switching energy (Esw), clarifying a clearer internal relationship between reverse recovery and junction temperature. Meanwhile, the aforementioned critical parameters are further analyzed on an electrical scale with normal atmosphere temperature, including switching speed range of 62.3–2054.8 A/μs, load current range of 6–30 A, and dc voltage range of 400–1000 V. Third, based on newly proposed power loss analysis method, the continuous operation performance of SiC diodes is quantified and analyzed in actual cryogenic converters. The excellent temperature dependence indicates that SiC diodes have great superiority for extreme applications. Importantly, SiC mosfet's body diode shows the great potential to operate as a freewheeling diode in the compact converter, especially at cryogenic temperature. [ABSTRACT FROM AUTHOR]

A novel cobweb-like disk resonator gyroscope (CDRG) with a very small frequency split between two degenerate modes has been designed and implemented. In comparison with the ring-like DRG (RDRG), the CDRG has fewer fabrication imperfections owing to its all-linear structure. In addition, the CDRG displays a superior nonlinear effect compared with the RDRG, and internal differential electrode excitation and detection were used to further reduce the nonlinear effect. The CDRGs and RDRGs were placed side by side on the same wafer, and the characteristics of these as-fabricated resonators were then tested. The results showed that the resonant frequencies and Q-factors of the CDRGs and RDRGs were approximately 18 kHz and nearly 100k, respectively. The smallest as-fabricated relative frequency split (29.9 ppm) of the CDRGs was about 10.8 times smaller than that (322.5 ppm) of an RDRG built side by side on the same wafer, which had the lowest relative frequency split among all current disk resonator gyros. Finally, the preliminary results for the performance of the CDRG and RDRG in the force-to-rebalance mode and mode matching are given. Under the same conditions, the maximum vibration displacement, scale factor, angular random walk, and bias instability of the CDRG were improved by 62.8%, 112%, 700%, and 314%, respectively, compared with the RDRG. [ABSTRACT FROM AUTHOR]

p+-Si/n-Zn2SiO4 heterojunction diodes were fabricated on Si substrate, and tested as X-ray detector for the first time in this letter. The devices exhibited good rectification properties at dark current, and the dark current density was $\sim 5.6\times 10^{\mathbf {-6}}$ A/cm2 at −40 V. An obvious response to X-ray illumination (generated by bremsstrahlung with a tungsten target with tube voltage 30 kV) was observed at reversed bias, and the photo-to-dark ratio exceeding 480 was achieved. Furthermore, the detector exhibited both photoconductive behavior and photovoltaic behavior to switching X-ray illumination, and response time and recovery time are discussed on both mechanisms. In addition, the detector showed fast response time less than 200 ms and the linear outputs against incident X-ray dose rate from 0.383 Gy/s to 4.596 Gy/s at zero-bias voltage. The results imply that the ultra-wide band gap Zn2SiO4 based junction-type detectors have the potential for passive X-ray dose detection and nuclear battery cell applications. [ABSTRACT FROM AUTHOR]

In this article, the static, dynamic, and short-circuit properties of 1.2-kV commercial 4H-SiC planar and trench gate metal–oxide–semiconductor field-effect transistors (MOSFETs) are compared and analyzed in a wide temperature range from 90 to 493 K. The temperature-dependent specific ON-resistance (${R}_{\text {sp}- \mathrm{\scriptscriptstyle ON}}$) and threshold voltage (${V}_{\text {th}}$) are analyzed in relation to the density of the interface state. The turn-on rise and turn-off fall times (${T}_{r}$ and ${T}_{f}$) and the corresponding energy loss (${E}_{r}$ and ${E}_{f}$) are extracted from a double-pulse test from cryogenic to high temperature and analyzed. The short-circuit capability of the two structures is studied at low temperature for the first time. The comprehensive comparison and analysis of the planar and trench gate MOSFET versus temperature in this work show the importance to study applications with SiC MOSFETs in a wide temperature range, especially for the cryogenic temperatures. [ABSTRACT FROM AUTHOR]

Frequency symmetry of a cobweb-like disk resonator gyroscope (CDRG) has been compared with a conventional ring-like disk resonant gyroscope (RDRG) in this letter to corroborate that linear beam structures have a better process tolerance than curved beam structures for micro-fabrication processes. The CDRG comprises multiple concentric cobweb-like rings and each is formed by 16 identical straight beams joined end-to-end. It exhibits as-fabricated symmetric vibration behavior superior to RDRGs. To compare as-fabricated structural symmetry, CDRG and RDRG are placed side-by-side on the same wafer and simulated using COMSOL. A tested frequency split as low as 0.56 Hz is achieved for CDRG, and the average relative frequency split is 79.7 ppm, which is approximately seven times smaller than that of RDRG. Additionally, a temperature characteristics test demonstrates that the as-fabricated CDRG has excellent temperature stability, and the relative frequency split varied by 2.83 ppm in the temperature ranging from −20 °C to +80 °C. The proposed concept is verified by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a dual quantization lateral-axis capacitive electromechanical sigma–delta modulator (EM- \Sigma \Delta \mathrm M ) vibratory wheel gyroscope under mode-matched condition. A symmetric wheel gyroscope structure was designed, fabricated, and wafer-level packaged under vacuum. The EM- \Sigma \Delta \mathrm M interface loop adopts a fourth-order multifeedback and local resonator \Sigma \Delta \mathrm M noise shaping structure, taking advantage of single-bit and multibit quantization in a single-loop modulator. To evaluate the influence of quantization noise, various numbers of bits of the multibit quantizator were compared and the optimal number of bits was calculated. The interface circuit system was implemented in hardware based on a low-noise front-end application-specified integrated circuit and a back-end discrete-time EM- \Sigma \Delta \mathrm M realized in a field-programmable gate array chip. The system clock was generated using a self-clocking scheme, which allows interfacing to gyroscope with a wide range of drive frequencies. Experimental evaluation indicated that the digital gyroscope system achieved a scale factor of 2073LSB(4.1 mV)/deg/s, with a nonlinearity of 0.046%, a noise floor of 3.1 m°/s/ $\surd $ Hz within a bandwidth of 100 Hz, and a bias instability of 1.3 deg/hr. [2017-0081] [ABSTRACT FROM PUBLISHER]