Effects of Thermal Boundary Resistance on Thermal Management of Gallium-Nitride-Based Semiconductor Devices: A Review

Wide-bandgap gallium nitride (GaN)-based semiconductors offer significant advantages over traditional Si-based semiconductors in terms of high-power and high-frequency operations. As it has superior properties, such as high operating temperatures, high-frequency operation, high breakdown electric field, and enhanced radiation resistance, GaN is applied in various fields, such as power electronic devices, renewable energy systems, light-emitting diodes, and radio frequency (RF) electronic devices. For example, GaN-based high-electron-mobility transistors (HEMTs) are used widely in various applications, such as 5G cellular networks, satellite communication, and radar systems. When a current flows through the transistor channels during operation, the self-heating effect (SHE) deriving from joule heat generation causes a significant increase in the temperature. Increases in the channel temperature reduce the carrier mobility and cause a shift in the threshold voltage, resulting in significant performance degradation. Moreover, temperature increases cause substantial lifetime reductions. Accordingly, GaN-based HEMTs are operated at a low power, although they have demonstrated high RF output power potential. The SHE is expected to be even more important in future advanced technology designs, such as gate-all-around field-effect transistor (GAAFET) and three-dimensional (3D) IC architectures. Materials with high thermal conductivities, such as silicon carbide (SiC) and diamond, are good candidates as substrates for heat dissipation in GaN-based semiconductors. However, the thermal boundary resistance (TBR) of the GaN/substrate interface is a bottleneck for heat dissipation. This bottleneck should be reduced optimally to enable full employment of the high thermal conductivity of the substrates. Here, we comprehensively review the experimental and simulation studies that report TBRs in GaN-on-SiC and GaN-on-diamond devices. The effects of the growth methods, growth conditions, integration methods, and interlayer structures on the TBR are summarized. This study provides guidelines for decreasing the TBR for thermal management in the design and implementation of GaN-based semiconductor devices

A composite quality-guided phase unwrapping algorithm for fast 3D profile measurement

Fringe pattern profilometry (FPP) is one of the most promising 3D profile measurement techniques, which has been widely applied in many areas. A challenge problem associated with FPP is the unwrapping of wrapped phase maps resulted from complex object surface shapes. Although existing quality-guided phase unwrapping algorithms are able to solve such a problem, they are usually extensively computational expensive and not able to be applied to fast 3D measurement scenarios. This paper proposes a new quality-guided phase unwrapping algorithm with higher computational efficiency than the conventional ones. In the proposed method, a threshold of quality value is used to classify pixels on the phase maps into two types: high quality (HQ) pixels corresponding to smooth phase changes and low quality (LQ) ones to rough phase variance. In order to improve the computational efficiency, the HQ pixels are unwrapped by a computationally efficient fast phase unwrapping algorithm, and the LQ pixels are unwrapped by computational expensive flood-fill algorithm. Experiments show that the proposed approach is able to recover complex phase maps with the similar accuracy performance as the conventional quality-guided phase unwrapping algorithm but is much faster than the later. © 2012 SPIE

3D shape measurement based on projection of triangular patterns of two selected frequencies

In this paper, a temporal shift unwrapping technique is presented for solving the problem of shift wrapping associated with spatial shift estimation (SSE)-based fringe pattern profilometry (FPP). Based on this technique, a novel 3D shape measurement method is proposed, where triangular patterns of two different spatial frequencies are projected. The patterns of the higher frequency are used to implement the FPP, and the one with lower frequency is utilized to achieve shift unwrapping. The proposed method is able to solve the shift unwrapping problem associated with the existing multi-step triangular pattern FPP by projection of an additional fringe pattern. The effectiveness of the proposed method is verified by experimental results, where the same accuracy as existing multi-step triangular pattern FPP can be achieved, but enabling the measurement of objects with complex surface shape and high steps

Improved geometrical model of fringe projection profilometry

The accuracy performance of fringe projection profilometry (FPP) depends on accurate phase-to-height (PTH) mapping and system calibration. The existing PTH mapping is derived based on the condition that the plane formed by axes of camera and projector is perpendicular to the reference plane, and measurement error occurs when the condition is not met. In this paper, a new geometric model for FPP is presented to lift the condition, resulting in a new PTH mapping relationship. The new model involves seven parameters, and a new system calibration method is proposed to determine their values. Experiments are conducted to verify the performance of the proposed technique, showing a noticeable improvement in the accuracy of 3D shape measurement

Shadow removal method for phase-shifting profilometry

In a typical phase-shifting profilometry system for the three-dimensional (3D) shape measurement, shadows often exist in the captured images as the camera and projector probe the object from different directions. The shadow areas do not reflect the fringe patterns which will cause errors in the measurement results. This paper proposed a new method to remove the shadow areas from taking part in the 3D measurement. With the system calibrated and the object reconstructed, the 3D results are mapped on a point-by-point basis into the corresponding positions on the digital micro-mirror device (DMD) of the projector. A set of roles are presented to detect the shadow points based on their mapped positions on the DMD plane. Experimental results are presented to verify the effectiveness of the proposed method

Chronique d'Egypte : bulletin périodique de la Fondation Egyptologique Reine Elisabeth

Phase shifting profilometry (PSP) technique is widely used as a 3-D shape measurement technique due to its robustness and accuracy. However, PSP requires multiple fringe pattern images to be projected onto an object and a reference plane to calculate the phase value, and also the object must maintain motionless when the measurement is taken. If the object moves during the measurement, significant errors will be introduced when calculating the phase value. This paper analyses the relationship between the object movement and the phase value, and proposes a method for compensating the errors caused by two-dimensional movement of object. This method can eliminate the errors caused by two-dimensional movement of object and reconstruct the object shape successfully. The effectiveness of the proposed method is verified by simulations. © 2012 SPIE

An object image edge detection based quality-guided phase unwrapping approach for fast three-dimensional measurement

A new approach for achieving fast and reliable unwrapping of complex phase maps is presented for phase shifted based three-dimensional (3D) Fringe pattern profilometry (FPP). As phase unwrapping errors are often caused by shadows on fringe patterns images and object surface discontinuities, we propose to identify both of them. An image of the object is acquired by averaging the fringe patterns reflected from the object surface, based on which shadow areas and the phase discontinuities are identified. When carrying out phase unwrapping, the shadow areas and the edge pixels will be isolated, and then the remaining areas are unwrapped by means of an efficient technique proposed below. All the remaining pixels are then unwrapped by an efficient technique proposed, by which, the computational efficiency can be significantly improved. As proven by the experiment results, the proposed approach is able to implement fast and reliable phase unwrapping

LncRNA-RMRP Acts as an Oncogene in Lung Cancer.

Accumulating studies have demonstrated that long noncoding RNAs (lncRNAs) act a crucial role in the development of tumors. However, the role of lncRNAs in lung cancer remains largely unknown. In this study, we demonstrated that theexpression of RMRP was upregulated in lung adenocarcinoma tissues compared to the matched adjacent normal tissues. Moreover, of 35 lung adenocarcinoma samples, RMRP expression was upregulated in 25 cases (25/35; 71.4%) compared to the adjacent normal tissues. We also showed that RMRP expression was upregulated in lung adenocarcinoma cell lines (A549, SPC-A1, H1299 and H23) compared to the bronchial epithelial cell line (16HBE). Ectopic expression of RMRP promoted lung adenocarcinoma cell proliferation, colony formation and invasion. In addition, overexpression of RMRP inhibited the miR-206 expression in the H1299 cell and increased the KRAS, FMNL2 and SOX9 expression, which were the target genes of miR-206. Re-expression of miR-206 reversed the RMRP-induced the H1299 cell proliferation and migration. Our data proved that RMRP acted as an oncogene LncRNA to promote the expression of KRAS, FMNL2 and SOX9 by inhibiting miR-206 expression in lung cancer. These data suggested that RMRP might serve as a therapeutic target in lung adenocarcinoma