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We propose a substrate with high thermal conductivity, manufactured by the low‐temperature co‐fired ceramic (LTCC) multilayer circuit process technology, as a new DC/DC converter platform for power electronics applications. We compare the reliability and power conversion efficiency of a converter using the LTCC substrate with the one using a conventional printed circuit board (PCB) substrate, to demonstrate the superior characteristics of the LTCC substrates. The power conversion efficiencies of the LTCC‐ and PCB‐based synchronous buck converters are 95.5% and 94.5%, respectively, while those of nonsynchronous buck converters are 92.5% and 91.3%, respectively, at an output power of 100 W. To verify the reliability of the LTCC‐based converter, two types of tests were conducted. Storage temperature tests were conducted at −20 °C and 85 °C for 100 h each. The variation in efficiency after the tests was less than 0.3%. A working temperature test was conducted for 60 min, and the temperature of the converter was saturated at 58.2 °C without a decrease in efficiency. These results demonstrate the applicability of LTCC as a substrate for power conversion systems.

We propose a multilayered-substrate-based power semiconductor discrete device package for a low switching loss and high heat dissipation. To verify the proposed package, cost-effective, low-temperature co-fired ceramic, multilayered substrates are used. A bare die is attached to an embedded cavity of the multilayered substrate. Because the height of the pad on the top plane of the die and the signal line on the substrate are the same, the length of the bond wires can be shortened. A large number of thermal vias with a high thermal conductivity are embedded in the multilayered substrate to increase the heat dissipation rate of the package. The packaged silicon carbide Schottky barrier diode satisfies the reliability testing of a high-temperature storage life and temperature humidity bias. At 175 degrees C, the forward current is 7 A at a forward voltage of 1.13V, and the reverse leakage current is below 100A up to a reverse voltage of 980V. The measured maximum reverse current (I-RM), reverse recovery time (T-rr), and reverse recovery charge (Q(rr)) are 2.4 A, 16.6ns, and 19.92 nC, respectively, at a reverse voltage of 300V and di/dt equal to 300 A/s.

We propose a dual output dc/dc converter for high efficiency and small form factor in electric bike applications. To implement a converter with single input of 48 V and dual output of 5 V and 12 V, we propose the system architecture combined with a 48-to-12 V converter and a 12-to-5 V converter on single PCB. The input of the 12-to-5 V is connected to the output of the 48-to-12 V converter to obtain stable 5 V without regard to the battery voltage. For high efficiency, both converters use synchronous topologies. For small form factor, the switching frequencies of the converters are fixed to 300 kHz and 1 MHz, respectively. To minimize undesirable PCB noise, several resistors are added and signal paths are designed shortly. The proposed dual output converter was implemented to 45 mm × 42 mm size. When the input voltage of 48 V is supplied, the measure efficiency is 87.5 % under a full-load condition of 3.1 A at 5 V output and 2 A at 12 V output.

The combination of a recessed-gate structure and CF4 plasma treatment was studied to realize a normally-off operation of a AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistor (MIS-HEMT) for power electronics applications. We verified that fluorine ions incorporated with a strong electronegativity increase the threshold voltage (Vth). In addition, CF4 plasma treatment slightly etches the AlGaN surface as deeply as 25 A. A fabricated device exhibits a threshold voltage of as high as 2.6 V. Using a combination of gate recess and plasma treatment processes, the device demonstrates a tremendous potential of normally-off AlGaN/GaN MIS-HEMTs for power electronics applications.

We propose pulse-mode dynamic Ron measurement as a method for analyzing the effect of stress on large-scale high-power AlGaN/GaN HFETs. The measurements were carried out under the soft-switching condition (zerovoltage switching) and aimed to minimize the self-heating problem that exists with the conventional hard-switching measurement. The dynamic R-on of the fabricated AlGaN /GaN MIS-HFETs was measured under different stabilization time conditions. To do so, the drain-gate bias is set to zero after applying the off-state stress. As the stabilization time increased from 0.1 mu s to 100 ms, the dynamic R-on decreased from 160 Omega to 2 Omega. This method will be useful in developing high-performance GaN power FETs suitable for use in high-efficiency converter/inverter topology design.

A large GaN-Schottky barrier diode (SBD) with a recessed dual anode metal is proposed to achieve improved the forward characteristics without a degradation of the reverse performances. Using optimized dry etch condition for a large device, the electrical characteristics of the device are demonstrated when applying the recessed dual anode metal and changing the recess depths. The device size and channel width are 4 mm2 and 63 mm, respectively. The 16-nm recessed dual anode metal SBD has a turn- on voltage of 0.34 V, a breakdown voltage of 802 V, and a reverse leakage current of $1.82~\mu \text{A}$ /mm at −15 V. The packaged SBD exhibits a forward current of 6.2 A at 2 V and a reverse recovery charge of 11.54 nC.

A sub-ppm level MEMS gas sensor that can be used for the detection of formaldehyde (HCHO) is presented. It is realized by using a zinc oxide (ZnO) thin-film material with a Ni-seed layer as a sensing material and by bulk micromachining technology. To enhance sensitivity of the MEMS gas sensor with Ni-seed layer was embedded with ZnO sensing material and sensing electrodes. As experimental results, the changed sensor resistance ratio for HCHO gas was 9.65 % for 10 ppb, 18.06 % for 100 ppb, and 35.7 % for 1 ppm, respectively. In addition, the minimum detection level of the fabricated MEMS gas sensor was 10 ppb for the HCHO gas. And the measured output voltage was about 0.94 V for 10 ppb HCHO gas concentration. The noise level of the fabricated MEMS gas sensor was about 50 mV. The response and recovery times were 3 and 5 min, respectively. The consumption power of the Pt micro-heater under sensor testing was 184 mW and its operating temperature was .

This paper presents a micromachined air-gap structure microelectromechanical systems (MEMS) acoustic sensor, which is fabricated via assisted high-speed lateral etching and chemical mechanical polishing (CMP). A sandwich structure (LTO/P2O5/LTO) as a sacrificial layer for the releasing process is proposed to produce an air-gap structure MEMS acoustic sensor. This sandwich structure can be etched selectively in a specific patterned P2O5 layer. In addition, the sandwich structure proved superior to using only low temperature oxide (LTO) layer for the releasing process. We confirmed that the proposed releasing method assisted by lateral etching and CMP is very effective for creating a clean air-gap cavity in MEMS devices. In this work, the air-gap structure MEMS acoustic sensor is based on the capacitance change of a movable thin poly-silicon membrane. A high-gain impedance converter was mounted on a printed circuit board (PCB) with a silicon MEMS acoustic sensor to transform the electrical signal for input acoustic pressure. The membrane size of the MEMS acoustic sensor was 1.5 × 1.5 mm2. The sensitivity achieved was about 0.018–5.17 mV Pa−1. The noise level of the fabricated device was 10 µV Pa−1.

The electronic industries have been tried to develop the electronic packaging technology for high-density, light weight, and miniaturization of mobile personal information terminals such as notebook PC, personal digital assistant (PDA), or handheld PC as the performance and the portability of the system have been become important more and more. The generated heat from the CPU of the electronic system should be dissipated effectively for the stability in operation and the long life-time of the system. In the present study, micro-heat pipes (MHPs) with cross-section of polygon have been manufactured and tested for operating characteristics and heat transfer limit. An additional process for installing a wick that is an inevitable component of heat pipes is not required for the MHP. For a small-sized heat pipe in the present study, a high precision technology is needed in manufacturing process. The MHPs tested in this paper have a triangular cross-section with curved sides and a rectangular cross-section with curved sides. The material of the MHP is copper and the working fluid of it is pure water. The test was performed in a vacuum chamber to minimize heat loss. The operating temperatures of the MHP were considered from 60 to 90 °C. From the test results, the MHP with triangular cross-section can dissipate up to a thermal load of 7 W.

This paper reports on a 3 mm ×3 mm ×0.003 mm piezoelectric membrane acoustic device, which works as a microphone and a microspeaker. It has a 0.5 μm thick zinc oxide (ZnO) piezoelectric thin film on a 1.5 μm thick low-stress silicon nitride membrane, made of LPCVD. The maximum deflection in the center of membrane, using laser Doppler vibrometer (LDV), is 1 μm at 7.3 kHz with input drive 15 V0-P (zero-peak). The output sound pressure level (SPL) of microspeaker is 76.3 dB SPL at 7.3 kHz, and 83.1 dB SPL at 13.3 kHz with input drive 15 V0-P. The distance between the reference microphone and piezoelectric microspeaker is 1 cm. The sensitivity of the microphone is 0.51 mV/Pa at 7.3 kHz with noise level of 18 dB SPL.

A compact 10 ~ 13 GHz low-noise amplifier (LNA) monolithic microwave integrated circuit (MMIC) using simple matching and bias circuits is designed and fabricated using AlGaN/GaN 0.25 μm high electron mobility transistor (HEMT) technology on silicon carbide (SiC) substrate. In order to reduce the chip size and simplify the structure of the LNA, the matching and bias circuits were combined functionally and structurally together and the meandered microstriplines were used. And the combined circuits also contributed to decrease the noise figure of the LNA. Therefore, the measured noise figures of the LNA are almost equal to the minimum noise figure of 2 x 100 μm device which was used for the first stage of the LNA. And also the chip size of the fabricated LNA is 1.7 x 0.8 mm 2 including two ground- signal-ground (GSG) pads and the DC pads on the chip. The LNA shows a noise figure of 1.7 ~ 2.1 dB with a gain of 19 ~ 26 dB across the 10 ~ 13 GHz frequency range. In continuous wave (CW) conditions, it presents a saturated output power of 29 ~ 34 dBm for 10 ~ 13 GHz and also the output third-order intercept point (OIP3) of 42 dBm at 11.4 GHz.

Even when there is a sufficient heat dissipation area from the heat sink to the environment, if the heat flux in the chip package substrate cannot be transferred rapidly to the heat sink, a thermal problem may occur.[1] In this study, a relatively thin CPV module compared to general models was considered. Because four solar chips are mounted on a center column in the CPV module, heat can accumulate rapidly. Therefore, a heat pipe with high thermal conductivity was considered as the heat dissipation method.[2] The heat pipe adopted in the present study is commercially available and has a circular type sintered wick in it. To apply the heat pipe to the CPV module with thin thickness and a central column with 4 solar cells, it should be pressed and bent. The thermal characteristics of the pressed and bent heat pipe was investigated experimentally.

We present a method of forming shallow p-doping on a 4H-SiC surface by depositing a thin Al layer (d = 5 nm) and then thermally annealing it at 1000 °C for 10 min. A secondary ion mass spectrometry analysis of the annealed Al/SiC sample reveals an Al concentration in excess of 1017 cm−3 up to a depth of d ≤ 250 nm. I–V measurements and CV characterizations of Ti-SiC Schottky barrier diodes (SBDs) fabricated on a n-type SiC epi-wafer indicate that the shallow Al doping increases the built-in potential of the junction and the barrier height by ΔVbi=0.51 eV and ΔϕB=0.26 eV, respectively. Assuming a rectangular doping profile, calculations of the built-in voltage shift and the Schottky barrier height indicate that partial dopant activation (activation ratio ∼2%) can induce the observed barrier height shift. The shallow doping method was then used to fabricate junction terminations in SBDs which increased the breakdown voltage and reduced the reverse leakage current. Technology CAD simulations of the SBD with ...

A low onset voltage AlGaN/GaN diode with a width of 14 mm is achieved. The recess depth of the AlGaN layer is responsible for the low onset voltage. In comparison with the conventional non-recessed diode, the onset voltage reduces by 45% along with a decrease of reverse leakage current by about one order of magnitude.

Bonding-pad electrode-area-etched AlGaN/GaN on a Si-based Schottky barrier diode (SBD) is fabricated. Electrode mesa etching leads to reverse bias leakage current about one order of magnitude lower than that of SBD without electrode mesa etching, but forward currents do not vary greatly, compared with that in conventional SBD, which has no electrode mesa etching.

Al2O3 passivation by thermal oxidation of aluminium on AlGaN/GaN high-electron-mobility transistors (HEMTs) without Al2O3 etching is proposed. The deposition of a 5-nm-thick Al film was carried out, followed by a lift-off process to remove Al from the ohmic and contact pad area. Subsequently, the Al film was annealed under O2 ambient. When the gate bias was −7 V, the gate leakage currents of a conventional nonpassivated HEMT, a surface-passivated Schottky-gate HEMT, and a surface-passivated MOS-HEMT were determined as 140, 96, and 4.1 µA/mm, respectively. The current collapse phenomenon in the Al2O3-surface-passivated devices was evidently suppressed compared with that in the nonpassivated HEMT.

A monolithic electronic nose system, which has 12 independent channels, was fabricated by post CMOS micromachining process. Read-out integrated circuits were fabricated with the standard CMOS processes with design rule of 0.8 mum. And, the MEMS parts of the electronic nose were fabricated by hybrid etching, composed of bulk micromachining with TMAH (tetramethy lammonium hydroxide) and deep dry etching, on the backside of the wafer after the CMOS processes. Resistance matching circuit, instrumentation amplifier, multiplexer, and transducer circuits with bridge structure were included in the read-out circuitry. And, heat control circuits were also implanted in the monolithic circuit to maintain the temperature of the MEMS sensing parts as constant. Carbon black-polymer composites and Au nano-particles were used as sensor materials. The MEMS parts of the electronic nose were designed to have well-shaped structures. These structures are considered to be suitable for drop coating procedure

High throughput near-field optical cantilever probe is prepared for high-density recording. Multiaperture cantilever is designed to enhance data transfer rate. Two-legged cantilever is proposed to regulate distances between the tips and media.

This paper reports the 3/spl times/3/spl times/0.003 mm/sup 3/ piezoelectric membrane acoustic device, which works as a microphone and a microspeaker. It has a 0.5 /spl mu/m thick zinc oxide (ZnO) piezoelectric thin film on a 1.5 /spl mu/m thick low stress silicon nitride membrane, made of LPCVD. The maximum deflection in the center of membrane, using laser Doppler vibrometer, is 1 /spl mu/m at 7.3 kHz with input drive 15 V/sub P-K/ (zero-peak). The output sound pressure level (SPL) of microspeaker is 76.3 dB SPL at 7.3 kHz, and 83.1 dB SPL at 13.3 kHz with input drive 15 V. The distance between reference microphone and piezoelectric microspeaker is 1 cm. The sensitivity of microphone is 0.51 mV/Pa at 7.3 kHz with noise level of 18 dB SPL.

This paper presents a micromachined stress-free through silicon via (TSV) backend process for AlGaN/GaN-on-Si (1 1 1) platform-based devices, which was processed by assisted back grinding, chemical mechanical polishing, deep reactive ion etching (DRIE) and copper (Cu) electroplating for the TSV. The metal-filled TSV structure was formed to enhance thermal conduction from the frontend terminal to the backend terminal, especially the source region of the AlGaN/GaN-on-Si (1 1 1) platform-based RF power devices. At the end of a stress-free TSV dry etching process, we have changed RF power 600 W to 300 W to minimize thermal stress of the fabricated TSV electrode pad structure of the AlGaN/GaN-on-Si platform-based devices. Additionally, we have sputtered a multi-metal layer and electroplated Cu metal to interconnect a topside electrode to TSV. To protect the thinned TSV electrode pad structure from water pressure in a sawing process, we have covered photoresist (AZ4330RS) of 3.3 µm thickness on the top area of the structures. We confirmed that the proposed TSV formation method assisted by low-power operation DRIE and protection of the thinned TSV surface by using the thick photoresist is very effective to create minimally stressed TSV structures in AlGaN/GaN-on-Si platform-based devices. The improvement was proved by the yield of dice without bursting the pad structures on a 4 inch AlGaN/GaN-on-Si wafer.

A capacitive MEMS acoustic sensor with two sacrificial layers based on surface micromachining on a GaAs substrate is presented. This sensor has bottom electrode anchors fabricated using an initial sacrificial layer for the formation of a back chamber. The bottom anchors serve to eliminate the back side process of the wafer for a conventional back chamber because the chamber is implemented through substrate surface etching. The proposed circular-type microphone has a diameter of 1.0 mm and a gap height of 2 µm. It shows a pull down voltage of 8.5 V and a total capacitance of 5.5 pF. Additionally, the MEMS microphone has a sensitivity of 0.09 mV/Pa at 1 kHz at a bias of 2 V.