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Measurements of dynamic characteristics of intermediate layer in thin semiconductors.
Park, Buhm,Jeon, Eun Beom,Kim, Hak-Sung,Kang, Namcheol,Park, Junhong American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.12
<P>A vibration test method for investigating the dynamic characteristics of thin multi-layered semiconductor wafers was proposed. Flash memory chips whose thickness was varied by grinding the wafers were used as specimens. The specimens composed of silicon, device, and device-protecting layers were excited at the clamped end by using a shaker attached to the clamping device. The vibration of the beam was measured using a laser vibrometer. The wave approach was used to analyze the vibration, from which the complex bending stiffness was determined. A theoretical model to obtain the dynamic characteristics (Young's modulus and the loss factor) of the intermediate device layer by using the measured bending stiffness was investigated. The results were examined and compared with those of a nanoindentation test to verify the accuracy of the model. The proposed method enabled determination of the dynamic properties of the intermediate layer without separation which are essential for understanding the impact response of the wafers during manufacturing process.</P>
Woojin Choi,Hojin Ryu,Namcheol Jeon,Minseong Lee,Ho-Young Cha,Kwang-Seok Seo IEEE 2014 IEEE electron device letters Vol.35 No.1
<P>In this letter, reduction of threshold voltage instability in gate recessed normally-off GaN metal insulator semiconductor high electron mobility transistors with SiN<SUB>x</SUB> gate insulator was investigated. A plasma enhanced atomic layer deposition technique was successfully employed for very thin SiN<SUB>x</SUB> (5 nm) as an interfacial layer. The hysteresis and drift of threshold voltage in transfer curve and the forward biased gate leakage current were effectively reduced.</P>
Structural effects on heat dissipation in InGaAs MHEMTs
Noh, Jinhyun,Ryoo, Yeonmi,Jeon, Namcheol,Cha, Ho-Young,Seo, Kwang-Seok Institute of Physics 2013 Semiconductor science and technology Vol.28 No.4
<P>Since the high thermal resistance of InGaAs metamorphic high electron mobility transistors (MHEMTs) limits their applicability, thermal management should be taken into account when designing the device structure. In this study, structural effects on heat dissipation in InGaAs MHEMTs were carefully investigated and experimentally validated. With an air bridge thickness of 10 µm and a gate pitch distance of 24 µm, the maximum channel temperature in a flip-chip bonded device was noticeably reduced from 132 to 106 °C (i.e. corresponding thermal resistance from 252.17 to 178.14 K W<SUP>−1</SUP>). Improved heat dissipation with the proposed structure was experimentally validated using backside-mounted devices by an infrared temperature measurement method.</P>
Jun-Chul Park,Jong-Gwan Yook,Bong Hyuk Park,Namcheol Jeon,Kwang-Seok Seo,Dongsu Kim,Woo-Sung Lee,Chan-Sei Yoo IEEE 2013 IEEE transactions on microwave theory and techniqu Vol.61 No.12
<P>This paper presents a gallium nitride (GaN)-based hybrid current-mode class-S (CMCS) power amplifier (PA) using a bandpass delta-sigma modulator (BPDSM) for a 955-MHz LTE signal. To enhance the drain efficiency of the CMCS PA, the chip-on-board (COB) technique, which can reduce the external parasitic components of the packaged transistor and allow fast switching operation at high frequencies by minimizing distortion of the pulse waveform, is adopted. Also, GaN Schottky barrier diodes are fabricated in-house to protect the switching transistor against the high negative voltage swing. The differential output filter and balun composed of lumped LC resonators are integrated at the back of the switching transistor to extract amplified LTE signal from the output rectangular waveform, and the fabricated CMCS PA is measured and analyzed at four different states of BPDSM according to the coding efficiency from different input power level to obtain higher power and efficiency. Finally, a cavity bandpass filter (BPF) is added to the output circuit for a more accurate reduction of the harmonics and out-of-band noise signals to enhance system efficiency. From the measured results for an 8.5-dB PAPR 3 G LTE 10-MHz input signal, the proposed CMCS PA has a maximum average output power of 37.61 and 30.78 dBm, and the resulting drain efficiencies of 33.3% and 38.6% with the drain voltage of 19 and 7 V, respectively.</P>