The thermal cross-talk in gallium nitride (GaN) high electron mobility transistor (HEMT) multifinger devices is a critical factor that limits their thermal performance, necessitating an in-depth investigation. In this study, the thermal cross-talk according to the number of gate fingers in GaN HEMT devices was analyzed. The number of gate fingers varied from 2 to 24, and the current density was set within a range of 8 W/mm to examine the operating temperatures of the devices. The results showed that the operating temperature of the device increased with higher current density and that the degree of thermal cross-talk was closely related to the number of fingers. When the number of fingers increased, the temperature of the device tended to increase sharply nonlinearly as the current density increased. Furthermore, it was observed that as the number of fingers increased, the temperature difference between the central and edge fingers increased, leading to a degradation in the uniformity of the device's temperature distribution. Additionally, at a low convective heat transfer coefficient, stable operation was impossible because the temperature of the device increased by more than 200 degrees C, and that for devices with 24 fingers to operate stably below 200 degrees C, a high convective heat transfer coefficient of 10,000 W/m2K or higher is required.

The thermal design and fabrication of a manifold microchannel structure for liquid cooling embedded in gallium nitride high electron mobility transistor radio frequency devices were investigated. Three microchannel designs with widths of 50, 100, and 200 mu m were assessed, and computational analysis was performed to evaluate their thermal performance and optimize the silicon carbide (SiC) substrate thickness. Consequently, the feasibility of the embedded microchannel structure was validated through an inductively coupled plasma-etching-based fabrication on a SiC substrate. The results showed that at maximum pumping power (P-pump), a smaller channel width exhibited better thermal performance, with a temperature difference of 28.3 degrees C. Subsequently, thickness optimization was conducted for the configuration with the best thermal performance structure of microchannel width (50 mu m) and fin width (50 mu m). The results indicated that at a low P-pump, a thicker channel tended to exhibit better thermal performance. However, at high P-pump, where thermal performance was improved, the optimal point was attained at a thinner structure with a thickness of 75 mu m. Furthermore, optimization of the etching process successfully eliminated micropillars formed when a large amount of SiC was etched, resulting in a smooth pillar-free microchannel structure.

GaN‐based high electron mobility transistors (HEMTs) is demonstrated using an extremely thin (≈ 5 nm) h‐BN passivation layer and air spacer, for the first time. The h‐BN passivation layer is grown by metal–organic chemical vapor deposition on top of the AlGaN barrier, followed by GaN‐based HEMTs fabrication. To prohibit the loss and/or damage of the thin h‐BN passivation layer, the SiN is deposited as a protection layer during the device fabrication. When the device fabrication is finalized, the SiN protection layer is removed by buffered oxide etchant, introducing the air spacer under the head of the T‐gate electrode. The electrical properties of the GaN‐based HEMTs applying h‐BN passivation layer and air spacer are measured and compared to the h‐BN/SiN passivated and conventional SiN passivated GaN‐based HEMTs. The difference of the DC characteristics corresponding to the passivation layer in GaN‐based HEMTs is negligible. However, compared to the conventional SiN passivated GaN‐based HEMTs, the RF performance, such as current gain cut‐off frequency and maximum oscillation frequency is improved by 50.3% and 68.5%, respectively, since the parasitic capacitances is reduced by the air spacer formation in GaN‐based HEMTs using a thin h‐BN passivation layer.

The effects of the parasitic gate capacitance and gate resistance (R-g) on the radiofrequency (RF) performance are investigated in L-G = 0.15 mu m GaN high-electron-mobility transistors with T-gate head size ranging from 0.83 to 1.08 mu m. When the device characteristics are compared, the difference in DC characteristics is negligible. The RF performance in terms of the current-gain cut-off frequency (f(T)) and maximum oscillation frequency (f(max)) substantially depend on the T-gate head size. For clarifying the T-gate head size dependence, small-signal modeling is conducted to extract the parasitic gate capacitance and R-g. When the T-gate head size is reduced from 1.08 to 0.83 mu m, R-g increases by 82%, while f(T) and f(max) improve by 27% and 26%, respectively, because the parasitic gate-source and gate-drain capacitances reduce by 19% and 43%, respectively. Therefore, minimizing the parasitic gate capacitance is more effective that reducing R-g in our transistor design and fabrication, leading to improved RF performance when reducing the T-gate head size.

Two-dimensional (2D) materials such as graphene and MoX 2 (X = S, Se, W, Te) are very important for the next-generation electronic devices. One of the most exciting materials in 2D materials is MoS 2 and the most important property that MoS 2 has, but graphene does not have, is the bandgap. For obtaining good quality of MoS 2 film, the selection of Mo precursor and S source is very important. And the other experimental conditions, such as synthesis temperature and reaction gas flow rate, are also important for obtaining good quality of MoS 2 thin film, particularly at low temperature. Synthesis of MoS 2 at the high temperature above 500 °C is relatively easy for the researchers. However, the synthesis of MoS 2 at the low temperature is not easy. In this work, we will report on the experimental results of MoS 2 synthesis carried out on SiO 2 (300 nm)/Si substrate at low temperature of 200 °C and 300 °C with precursor of Mo(CO) 6 . Even at the very low temperature of 200 °C, we could synthesize relatively good quality of MoS 2 films.

GaN-based high-electron-mobility transistors (HEMTs) are intensively researched for high-power radio frequency (RF), low noise, and aerospace applications, thanks to their high breakdown electric field, high carrier mobility and density at the hetero-interface, and wide bandgap [1-2]. For the improvement of RF performance, various approaches have been reported, including T-gate structure [3-4], surface passivation [5], n+-regrown source and drain contact [6], thin barrier structure [7], and graded-channel [8]. Among them, the T-gate structure has been extensively employed for the reduction of the gate resistance (Rg ) and thereby improvement of the RF performance. However, the usage of the wide T-gate structure enlarges parasitic gate capacitance components, which deteriorates the RF performance. As a result, one should pay careful attention to the dimension of the wide T-gate structure to reduce Rg as much as possible, not to enlarge the parasitic gate capacitance components. This motivates us to explore the optimum dimension of the wide T-gate structure in GaN-based HEMTs for X-band RF applications. To investigate the detailed impact of the gate resistance and parasitic gate capacitance components, we fabricated LG = 0.15 μm GaN-based HEMTs with various dimensions of the T-gate head from 0.5 to 0.8 μm during an e-beam lithography process step. The unit gate width (WG ) and number of gate finger (NF ) were 100 μm and 2, respectively. For comparison of the device characteristics with respect to the dimension of the gate head, DC and RF measurements were conducted for the fabricated GaN-based HEMTs with various dimensions of T-gate head. The DC characteristics in terms of the threshold voltage (VTH ), the maximum transconductance (gm,max ), and the saturation drain current (Id,sat ) were almost identical, regardless of the dimension of the T-gate head. On the contrary, the current-gain cut-off frequency (fT ) and maximum oscillation frequency (fMAX ) were improved by 26.5% and 21.0%, respectively, when the T-gate head size was reduced from 0.8 to 0.5 μm. In an effort of explore the origin of the dependence of the T-gate head on the RF performance, we have carried out small-signal modeling to extract the parasitic gate capacitance and gate resistance components from the measured RF data. As the T-gate head size was reduced from 0.8 to 0.5 μm, the gate-source parasitic capacitance component (Cgs_par ) was reduced by 19%, while the gate resistance component was increased by 32%. In our device design and fabrication, it turned out that the reduction of Cgs_par was more beneficial than the increase of Rg , leading to the improved RF performance with the gate head size decrease. In this work, our systematic research revealed that, unlike earlier reports [3-4], the reduction of the parasitic gate capacitance was essential for the improvement of the RF performance as opposed to the reduction of the gate resistance in LG = 0.15 μm GaN-based HEMTs for X-band RF applications. Acknowledgement This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MIST) (No. NRF-2021M3C1C3097672). References [1] T. Palacios, A. Chakraborty, S. Rajan, et al., “High-power AlGaN/GaN HEMTs for Ka-band applications,” IEEE Electron Device Lett., 2005, 26, 781-783. [2] K. Shinohara, D. C. Regan, Y. Tang, et al., “Scaling of GaN HEMTs and Schottky Diodes for Submillimeter-Wave MMIC Applications,” IEEE Trans. Electron Devices, 2013, 60, 2982-2996. [3] M. S. Cho, J. H. Seo, S. H. Lee, et al., “Fabrication of AlGaN/GaN Fin-Type HEMT Using a Novel T-Gate Process for Improved Radio-Frequency Performance,” IEEE Access, 2020, 6, 139156-139160. [4] X. W. Zhang, K. J. Jia, Y. G. Wang, et al., “AlNGaN HEMT T-Gate Optimal Design,” Applied Mechanics and Materials, 2013, 347, 1790-1792. [5] S.-J. Chang, H. W. Jung, J. W. Do, et al., “Enhanced Carrier Transport Properties in GaN-based Metal-Insulator-Semiconductor High Electron Mobility Transistor with SiN/Al2O3 bi-layer Passivation,” ECS J. Solid State Sci. Technol., 2018, 7, N89-N90. [6] T. Tang, K. Shinohara, D. Regan, et al., “Ultrahigh-speed GaN high-electron mobility transistors with fT/fmax of 454/444 GHz,” IEEE Electron Device Lett., 2015, 36, 549-551. [7] Y. Yue, Z. Hu, J. Guo, et al., “InAlN/AlN/GaN HEMTs with Regrown Ohmic Contacts and fT of 370 GHz,” IEEE Electron Device Lett., 2012, 33, 988-990. [8] J.-S. Moon, J. Wong, B. Grabar, et al., “360 GHz fMAX Graded-Channel AlGaN/GaN HEMTs for mmW Low-Noise Applications,” IEEE Electron Device Lett., 41, 1173-1176. Figure 1

Thermomechanical analysis of monolithic microwave integrated circuit (MMIC) packaging is essential to guarantee the reliability of radio frequency/microwave applications. However, a method for fast and accurate analysis of MMIC packaging structures has not been developed. Here, a machine learning (ML)-based solution for thermomechanical analysis of MMIC packaging is demonstrated. This ML-based solution analyzes temperature and thermal stresses considering key design parameters, including material properties, geometric characteristics, and thermal boundary conditions. Finite element simulation with the Monte Carlo method is utilized to prepare a large dataset for supervised learning and validation of the ML solution, and a laser-assisted thermal experiment is conducted to verify the accuracy of the simulation. After data preparation, regression tree ensemble and artificial neural network (ANN) learning models are investigated. The results show that the ANN model accurately predicts the outcomes with extremely low computing time by analyzing the high-dimensional dataset. Finally, the developed ML solution is deployed as a web application format for facile approaches. It is believed that this study will provide a guideline for developing ML-based solutions in chip packaging design technology.

Recently, we reported that device performance degradation mechanisms, which are generated by the γ-ray irradiation in GaN-based metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs), use extremely thin gate insulators. When the γ-ray was radiated, the total ionizing dose (TID) effects were generated and the device performance deteriorated. In this work, we investigated the device property alteration and its mechanisms, which were caused by the proton irradiation in GaN-based MIS-HEMTs for the 5 nm-thick Si3N4 and HfO2 gate insulator. The device property, such as threshold voltage, drain current, and transconductance varied by the proton irradiation. When the 5 nm-thick HfO2 layer was employed for the gate insulator, the threshold voltage shift was larger than that of the 5 nm-thick Si3N4 gate insulator, despite the HfO2 gate insulator exhibiting better radiation resistance compared to the Si3N4 gate insulator. On the other hand, the drain current and transconductance degradation were less for the 5 nm-thick HfO2 gate insulator. Unlike the γ-ray irradiation, our systematic research included pulse-mode stress measurements and carrier mobility extraction and revealed that the TID and displacement damage (DD) effects were simultaneously generated by the proton irradiation in GaN-based MIS-HEMTs. The degree of the device property alteration was determined by the competition or superposition of the TID and DD effects for the threshold voltage shift and drain current and transconductance deterioration, respectively. The device property alteration was diminished due to the reduction of the linear energy transfer with increasing irradiated proton energy. We also studied the frequency performance degradation that corresponded to the irradiated proton energy in GaN-based MIS-HEMTs using an extremely thin gate insulator.

As the package integration density increases, the demand for reducing the bond wire length and lowering the wire loop height is constantly increasing. As the wire loop height decreases, the wire's stiffness increases, minimizing wire collapse during the molding process and preventing damage due to the exposed wire beyond the molding during the marking process. At the same time, the shorter length of the wire reduces the inductance and resistance of the interconnection, thereby improving electrical characteristics during high-power signal transmission. Various studies have been performed on the wire low loop profiles, but most of them are for ball bonding which is the dominant process for wire bonding. There are no studies on loop formation, loop profile according to bonding process parameters, and corresponding loop height formed by wedge bonding. Therefore, in this study, a method of forming an ultra-low loop using a 1 mm thick gold wire by comparing and analyzing loop formation was proposed. In addition, the characteristics of the loop height based on a parametric study of the wedge bonding process were analyzed for the application of a highly integrated package or high-power package.

본 논문에서는 0.2 μm ETRI GaN HEMT 공정을 이용하여 RF 송수신기 모듈에 사용되는 X-대역 GaN monolithic microwave integrated circuit(MMIC) 저잡음 증폭기를 설계 및 제작하였다.피드백 마이크로스트립 선로를 트랜지스터 소 스에 적용하여 회로의 안정성을 확보함과 동시에 최대 가용이득 및 최적 잡음지수의 열화를 최소로 하는 입력

In this study, we fabricated a metamorphic high-electron-mobility transistor (mHEMT) device with a T-type gate structure for the implementation of W-band monolithic microwave integrated circuits (MMICs) and investigated its characteristics. To fabricate the mHEMT device, a recess process for etching of its Schottky layer was applied before gate metal deposition, and an e-beam lithography using a triple photoresist film for the T-gate structure was employed. We measured DC and RF characteristics of the fabricated device to verify the characteristics that can be used in W-band MMIC design. The mHEMT device exhibited DC characteristics such as a drain current density of 747 mA/mm, maximum transconductance of 1.354 S/mm, and pinch-off voltage of -0.42 V. Concerning the frequency characteristics, the device showed a cutoff frequency of 215 GHz and maximum oscillation frequency of 260 GHz, which provide sufficient performance for W-band MMIC design and fabrication. In addition, active and passive modeling was performed and its accuracy was evaluated by comparing the measured results. The developed mHEMT and device models could be used for the fabrication of W-band MMICs.

The impact of the passivation system on the device performance has been studied in GaN-based MIS-HEMTs using SiN/Al2O3 bi-layered passivation. The deposition of SiN and Al2O3 passivation layer induced the compressive and tensile stress on GaN channel layer, respectively. Through the Al2O3 deposition on top of SiN layer, the mechanical stress and device characteristics were modulated. The device properties such as carrier mobility and concentration at the hetero-interface were ameliorated when the slight tensile stress was applied on the GaN channel compared to the compressive stress. The proton radiation hardness corresponding to the passivation system was also researched. The SiN/Al2O3 passivation system exhibited stronger immunity to the proton radiation than that of SiN passivation due to the superior dielectric quality of Al2O3. These results highlight that the SiN/Al2O3 bi-layered passivation is promising technique for the optimization of the device performance and improvement of proton radiation hardness in GaN-based MIS-HEMTs.

Flexible, transparent and biocompatible polymer nanocomposite films can be fabricated using two-dimensional filler materials, which is of great interest for gas barrier applications. A bio-inspired polyvinyl alcohol (PVA) nanocomposite film was fabricated using sulfanilic acid group functionalized MXene (f-MXene) as the reinforcing filler and boric acid (BA) as the crosslinking agent. The f-MXene/BA/PVA nanocomposite films were characterized in terms of their thermal stability, mechanical properties and gas barrier efficacy, and the results indicated these were significantly improved compared to films made from pure PVA and MXene/BA/PVA nanocomposites. This is due to the homogeneous dispersion of the MXene and strong interfacial covalent bonds created by the BA crosslinkers between the f-MXene and the PVA matrix. The nanocomposite film consisting of 0.5 wt% f-MXene and 0.5 wt% BA (0.5 wt% f-MXene/BA/PVA) shows an oxygen permeability of similar to 0.73 x 10(-2) cc.cm/m(2).day.atm, which is a reduction of around 69% in gas permeability compared to that of a pure PVA film. In addition, the initial thermal decomposition temperature of the 0.5 wt% f-MXene/BA/PVA nanocomposite film increased from 257.4 degrees C to 288.2 degrees C. Futhermore, the tensile strength of the f-MXene/BA/PVA nanocomposite film improved by 67%, and the modulus was also increased by 49%. These results clearly suggest that the MXene/BA/PVA is an effective nanocomposite film when used as a high-performance gas barrier films. The functionalization of MXene and borate-crosslinking represents a practical method to improve the various properties of a range of polymers.

The device performance deterioration mechanism caused by the total ionizing dose effect after the γ-ray irradiation was investigated in GaN-based metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) for a 5 nm-thick SiN and HfO2 gate dielectric layer. The γ-ray radiation hardness according to the gate dielectric layer was also compared between the two different GaN-based MIS-HEMTs. Although HfO2 has exhibited strong tolerance to the total ionizing dose effect in Si-based devices, there is no detail report of the γ-ray radiation effects in GaN-based MIS-HEMTs employing a HfO2 gate dielectric layer. The pulsed-mode stress measurement results and carrier mobility behavior revealed that the device properties not only have direct current (DC) characteristics, but radio frequency (RF) performance has also been mostly degraded by the deterioration of the gate dielectric quality and the trapped charges inside the gate insulator. We also figured out that the immunity to the γ-ray radiation was improved when HfO2 was employed instead of SiN as a gate dielectric layer due to its stronger endurance to the γ-ray irradiation. Our results highlight that the application of a gate insulator that shows superior immunity to the γ-ray irradiation is a crucial factor for the improvement of the total ionizing dose effect in GaN-based MIS-HEMTs.

In this study, an E-band low-noise amplifier (LNA) monolithic microwave integrated circuit (MMIC) has been designed using silicon-germanium 130-nm bipolar complementary metal-oxide-semiconductor technology to suppress unwanted signal gain outside operating frequencies and improve the signal gain and noise figures at operating frequencies. The proposed impedance-controllable filter has series (R-s) and parallel (R-p) resistors instead of a conventional inductor-capacitor (L-C) filter without any resistor in an interstage matching circuit. Using the impedance-controllable filter instead of the conventional L-C filter, the unwanted high signal gains of the designed E-band LNA at frequencies of 54 GHz to 57 GHz are suppressed by 8 dB to 12 dB from 24 dB to 26 dB to 12 dB to 18 dB. The small-signal gainS(21)at the operating frequencies of 70 GHz to 95 GHz are only decreased by 1.4 dB to 2.4 dB from 21.6 dB to 25.4 dB to 19.2 dB to 24.0 dB. The fabricated E-band LNA MMIC with the proposed filter has a measuredS(21)of 16 dB to 21 dB, input matching (S-11) of -14 dB to -5 dB, and output matching (S-22) of -19 dB to -4 dB at E-band operating frequencies of 70 GHz to 95 GHz.