Chun Yen Tseng

Strong guided mode resonant local field enhanced visible harmonic generation in an azo-polymer resonant waveguide grating

Guided mode resonance (GMR) enhanced second- and third-harmonic generation (SHG and THG) is demonstrated in an azo-polymer resonant waveguide grating (RWG), comprised of a poled azo-polymer layer on top of a textured SU8 substrate with a thin intervening layer of TiO2. Strong SHG and THG outputs are observed by matching either in-coming fundamental- or out-going harmonic-wavelength to the GMR wavelengths of the azo-polymer RWG. Without the azo-polymer coating, pure TiO2 RWGs, do not generate any detectable SHG using a fundamental beam peak intensity of 2 MW/cm(2). Without the textured TiO2 layer, a planar poled azo-polymer layer results in 3650 times less SHG than the full nonlinear RWG structure under identical excitation conditions. Rigorous coupled-wave analysis calculations confirm that this enhancement of the nonlinear conversion is due to strong local electric fields that are generated at the interfaces of the TiO2 and azo-polymer layers when the RWG is excited at resonant wavelengths associated with both SHG and THG conversion processes.

High-Performance Depletion-Mode Multiple-Strip ZnO-Based Fin Field-Effect Transistors

To enhance the performances of the depletion-mode zinc-oxide (ZnO)-based MOSFETs, the multiple-channel and multiple-gate fin structures were deposited using the magnetron sputter system and patterned using the laser interference photolithography technique. The multiple-channel fin structure possessed the additional sidewall depletion width to enhance the gate controllability. The multiple-gate structure had a shorter source-gate distance and a shorter gate length between two gates to promote the gate operating performances. Therefore, the drain-source saturation current of the multiple-strip ZnO-based fin MOSFETs operated at a drain-source voltage of 10 V and a gate-source voltage of 0 V was improved to 13.7 mA/mm in comparison with 11.5 mA/mm of the conventional single-channel and single-gate ZnO-based MOSFETs. Furthermore, the corresponding maximum transconductance was enhanced from 4.1 to 6.9 mS/mm.

Nanomesh electrode on MgZnO-based metal-semiconductor-metal ultraviolet photodetectors.

In this work, the nano-scaled mesh electrodes are fabricated by obliquely depositing metals through the highly ordered polystyrene nanosphere mask. Furthermore, the intrinsic MgZnO film is deposited as the absorption layer for the metal-semiconductor-metal ultraviolet photodetectors (MSM-UV-PDs) using the vapor cooling condensation system. The 100-nm-linewidth nanomesh electrodes with metal occupying a roughly 10% of the device surface region consequently render PDs with a high transmittance in the ultraviolet (UV) wavelength range. The photoresponsivity of MgZnO-based MSM-UV-PDs evaluated at the wavelength of 330u2009nm with the operating bias voltage of 5u2009V is elevated from 0.135 to 0.248u2009A/W when the thin metal electrode is replaced by the nanomesh electrode, and the corresponding quantum efficiency is improved from 50.75 to 93.23%. Finally, adopting the nanomesh electrode also helps to enhance the UV-visible rejection ratio (R330nm/R450nm) and the detectivity from 1663 and 1.78u2009×u20091010u2009cmHz0.5W−1 to 2480 and 2.43u2009×u20091010u2009cmHz0.5W−1, respectively.

GaN-Based Enhancement-Mode Metal–Oxide–Semiconductor High-Electron Mobility Transistors Using LiNbO 3 Ferroelectric Insulator on Gate-Recessed Structure

To fabricate AlGaN/gallium nitride (GaN) enhancement-mode metal-oxide-semiconductor high-electron mobility transistors (E-MOSHEMTs), the gate-recessed structure and the LiNbO3 ferroelectric film were utilized in this paper. The LiNbO3 ferroelectric films deposited on the photoelectrochemically etched gate-recessed regions of the AlGaN/GaN E-MOSHEMTs as the gate insulator using a pulsed laser deposition system. The polarization-induced charges of the 2-D electron gas resided on the interface between the AlGaN and GaN layers could be modulated by the C+ domains of the crystalline (006) LiNbO3 ferroelectric films annealed in an oxygen ambience at 600°C for 30 min. When the 15-nm-thick AlGaN was formed in the gate-recessed regions, the threshold voltage and the maximum transconductance of the resulting gate-recessed LiNbO3/AlGaN/GaN E-MOSHEMTs were +0.40 V and 56.0 mS/mm, respectively. Furthermore, the flicker noise was the dominant noise in the resulting E-MOSHEMTs. The associated normalized low-frequency noise power density of 8.1 × 1011Hz-1 was measured.

Performance enhancement of multiple-gate ZnO metal-oxide-semiconductor field-effect transistors fabricated using self-aligned and laser interference photolithography techniques

The simple self-aligned photolithography technique and laser interference photolithography technique were proposed and utilized to fabricate multiple-gate ZnO metal-oxide-semiconductor field-effect transistors (MOSFETs). Since the multiple-gate structure could improve the electrical field distribution along the ZnO channel, the performance of the ZnO MOSFETs could be enhanced. The performance of the multiple-gate ZnO MOSFETs was better than that of the conventional single-gate ZnO MOSFETs. The higher the drain-source saturation current (12.41xa0mA/mm), the higher the transconductance (5.35 mS/mm) and the lower the anomalous off-current (5.7xa0μA/mm) for the multiple-gate ZnO MOSFETs were obtained.

Monolithic enhancement-mode and depletion-mode GaN-based MOSHEMTs

GaN-based metal-oxide-semiconductor high-electron-mobility transistors (MOSHEMTs) with outstanding properties of high operation speed and high breakdown voltage are promising for high frequency switching operation in ICs. To further develop the GaN-based digital ICs, the AlGaN/GaN MOSHEMT inverters integrated with the enhancement/depletion-mode (E/D-mode) transistors were investigated. In this work, the ferroelectric LiNbO3 (LNO) gate oxide layer and the photoelectrochemical (PEC)-recessed structure were simultaneously utilized to fabricate the critical E-mode AlGaN/GaN MOSHEMTs. Among the ferroelectric materials, the high dielectric constant LNO film with the larger spontaneous polarization of 80 μC/cm2, the wider bandgap of 3.9 eV, and the lower interface state density on the GaN-based semiconductor was beneficial to the modulation of the two-dimensional electron gas (2DEG) channel and the reduction of the gate leakage current. Besides, using the PEC-recessed structure could improve the transconductance of the E-mode transistors and adjust the operation current of the D-mode transistors without destroying the etched AlGaN surface. Instead of the typical tuning area size method, the PEC etching method was demonstrated in this work to adjust the current ratio (β) of the E/D-mode transistors with keeping the matched area size for the miniaturization of the AlGaN/GaN MOSHEMT inverters. From the voltage transfer curve, the corresponded VOUT was equaled to VIN = VDD/2 = 2.5 V, and the output swing were about 4.9 Vp-p as the input signal was 5 Vp-p. It revealed that the resulting AlGaN/GaN MOSHEMT inverter with the β of 25 was operated as a high performance un-skewed inverter.

ZnO-based multiple channel and multiple gate FinMOSFETs

In recent years, zinc oxide (ZnO)-based metal-oxide-semiconductor field-effect transistors (MOSFETs) have attracted much attention, because ZnO-based semiconductors possess several advantages, including large exciton binding energy, nontoxicity, biocompatibility, low material cost, and wide direct bandgap. Moreover, the ZnO-based MOSFET is one of most potential devices, due to the applications in microwave power amplifiers, logic circuits, large scale integrated circuits, and logic swing. In this study, to enhance the performances of the ZnO-based MOSFETs, the ZnObased multiple channel and multiple gate structured FinMOSFETs were fabricated using the simple laser interference photolithography method and the self-aligned photolithography method. The multiple channel structure possessed the additional sidewall depletion width control ability to improve the channel controllability, because the multiple channel sidewall portions were surrounded by the gate electrode. Furthermore, the multiple gate structure had a shorter distance between source and gate and a shorter gate length between two gates to enhance the gate operating performances. Besides, the shorter distance between source and gate could enhance the electron velocity in the channel fin structure of the multiple gate structure. In this work, ninety one channels and four gates were used in the FinMOSFETs. Consequently, the drain-source saturation current (IDSS) and maximum transconductance (gm) of the ZnO-based multiple channel and multiple gate structured FinFETs operated at a drain-source voltage (VDS) of 10 V and a gate-source voltage (VGS) of 0 V were respectively improved from 11.5 mA/mm to 13.7 mA/mm and from 4.1 mS/mm to 6.9 mS/mm in comparison with that of the conventional ZnO-based single channel and single gate MOSFETs.

Photoelectrochemically recessed AlGaN/GaN monolithic inverter incorporating LiNbO3 ferroelectric film

In this work, the AlGaN/GaN monolithic inverters were integrated by the enhancement-mode metal-oxide-semiconductor high-electron-mobility transistors (E-mode MOSHEMTs) and the depletion-mode metal-oxide-semiconductor high-electron-mobility transistors (D-mode MOSHEMTs). For the fabrication of the E-mode MOSHEMTs, the LiNbO3 (LNO) ferroelectric films deposited on the photoelectrochemically (PEC)-recessed structure effectively compensated the two dimensional electron gas (2DEG) channel existed in the AlGaN/GaN heterostructure. For the fabrication of the D-mode MOSHEMTs, the PEC wet etching method and the surface treatment were utilized to form the various-thick etched AlGaN layers with low surface defects. Therefore, the operating current of the D-mode MOSHEMTs could be controlled. Finally, the resulting monolithic inverters with a suitable current ratio (β) of 25 were successfully fabricated. The corresponded output swing (between VOH-VOL), the noise margin high (NMH: VOH-VIH), and the noise margin low (NML: VIL-VOL) were respectively about 4.9 V, 1.9 V, and 1.7 V, when the input signal was 5 Vp-p. Most importantly, the corresponded output voltage (Vout) was 2.5 V which equaled to the half of VDD according to the voltage transfer characteristics (VTC) of the resulting inverters, when the input voltage (VIN) was 2.5 V. It indicated that the monolithic inverters have an unskewed inverter property.