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The purpose of this study is to investigate the effects of electrical stress on the 1/ f noise behavior in n-channel metal–oxide–semiconductor transistors with ultrathin gate oxides. Even under a weak electrical stress, the drain current noise (Sid) of the device with a 1.4-nm-thick oxide was found to increase abruptly beyond a certain critical gate bias. This deteriorated noise property was proven to be from simultaneous increases in gate current noise (Sig) and the correlation between Sid and Sig, which were directly related to oxide trap generation and gate/drain current (Ig/Id) ratio, respectively. Meanwhile, the increase in Sid in the device with a 2.3-nm-thick oxide after stress, with a comparable transconductance degradation, was relatively insignificant because of the device's smaller Ig/Id ratio, even if the measured Sig was comparable to that of the thinner oxide device. Consequently, the 1/ f noise degradation could be much more significant than the accompanying DC characteristic degradations in the thin gate oxide below 1.5 nm.

The asymmetry between lower and upper intermodulation distortions (IMD) in a heterojunction bipolar transistor (HBT), which can be observed under certain baseband termination and bias conditions, is analyzed using a large-signal model. This approach enables harmonic balance analysis of IMD asymmetry in nonlinear circuits using HBTs and, therefore, overcomes the limitations of the conventional Volterra-series analysis. Closed-form expression derived from Volterra analysis is also employed to present comparisons with the large-signal model approach. Measurements indicate that the asymmetry is very sensitive to baseband termination, which varies with the envelope frequency of the input RF signal. Specifically, zero crossings of asymmetry are observed at each resonance frequency where the reactive part of baseband termination changes its sign rapidly. It is also found that the asymmetry is enhanced at a specific small bias current where the dominance of the 3rd order nonlinearity is greatly reduced by cancellation with the 2nd order nonlinearity. The bias condition for asymmetry occurrence is calculated, using a simple analytical equation, to be related to measurement data. All the measurements are verified successfully by nonlinear simulation using large-signal model. Finally, the advantage of the large-signal model approach compared to Volterra analysis for asymmetry prediction is discussed.

In this paper, we report the possibility of silicon (Si) plasma wave transistor (PWT) as a resonant terahertz (THz) emitter based on the theoretical analysis focusing on the strained Si with enhanced mobility. Under asymmetric boundary conditions for plasma wave instability, the amplitude of plasma wave in FET channel increases and this plasma wave increment provides the basis of the electromagnetic (EM) wave emission from FET. Because this instability is controlled by manipulation of plasma wave velocity (s) and electron drift velocity (0), we propose the design window based on s–0 plot which determines whether the device operates as the resonant THz emitters considering all the required physical conditions. It is expected from the proposed design window that strained Si PWT down to 10 nm gate length with enhanced channel mobility of 500 cm2V−1s−1 can operate as a resonant emitter in THz frequency range.

We study the influence of doping density and the resulting optimum operation voltage on the performance of quantum dot infrared photodetectors (QDIPs). The optimum operation voltage, where detectivity becomes maximum, becomes smaller as the doping density increases. This is because the optimum dark current levels are similar regardless of the doping density. We confirmed experimentally that the optimum dark current level is ∼5 mA (current density: ∼A/cm2) for our samples. It is found that the higher doping density improves the performance in the range used in this experiment (5×1016–5×1017/cm3). The response to a normal incident light is confirmed and the possibility of high-temperature operation of QDIP is shown.

An integrated optical/RF hybrid device was designed and fabricated for binary-phase-shift-keying (BPSK) subcarrier modulation. The device is composed of two identical high-speed multiple quantum well electroabsorption modulators branched with two multimode interference couplers. Using the device, we demonstrated that a RF subcarrier of 10 GHz is directly modulated in a BPSK scheme with an independently applied RF carrier and digital signal.

The velocity-mismatching effect of the traveling wave electroabsorption modulator (TWEAM) is investigated. A model is proposed to design the length of the modulator. Optical transmission through the device is simulated and the degradation of extinction ratio with velocity mismatch is analyzed.

A push-pull operation is proposed for low voltage actuation of a microelectromechanical (MEM) switch for RF application. The push-pull operation realized by torsion springs and contact electrode height amplification by leverage, lowers the actuation voltage of the MEM switch by reducing the gap between actuation electrodes. The proposed MEM switch is fabricated by gold surface micromachining. Switching operation up to 4 GHz is demonstrated. The actuation voltage is as low as 5 V. The insertion loss of ∼1 dB and the isolation as high as ∼40 dB at 1 GHz are achieved by the push-pull operation.

A new method of fabricating atomic force microscope (AFM) probe tip is presented. In this process, the probe tips were implemented using self-aligned heavily boron-doped silicon cantilevers in a bulk silicon wafer. In this structure, a stress-free cantilever can be easily defined by selective etch stop by the heavily boron-doped region in an anisotropic silicon etchant. The proposed tips do not require expensive silicon on insulator (SOI) wafers and double-side alignment. The probe tip dimensions can be exactly defined regardless of wafer thickness by the self-aligned etch from the front side. In addition, the cantilever thickness can be easily controlled by adjusting the diffusion time, and fabricated at low cost by using bulk silicon wafers. The fabricated probe tips showed resonant frequencies of 71.420 kHz with a 1.8-µm-thick probe tip and 122.660 kHz with a 3.0-µm-thick probe tip. Using the two fabricated probe tips, we successfully demonstrate image scanning of a 1 µm grating reference sample in contact and noncontact modes, respectively.

A linearization method for a multiple quantum well (MQW) electroabsorption analog modulator is studied. We analyze the nonlinear characteristics of the light-voltage (L-V) transfer curve in a MQW electroabsorption modulator and estimate its intermodulation distortion (IMD). We propose a novel linearization method, the integration of twin MQW modulators with optical 3 dB couplers. This method can reduce IMD2 and IMD3 simultaneously by only adjusting the modulation depth and the bias voltage of each modulator. Results of simulations show that the method can suppress IMD2 and IMD3 to below -65 dBc at a modulation depth of 10% without any serious loss of optical signal power or increase in chirp.

We fabricated a quantum dot infrared photodetector (QDIP) with 5-stacked self-organized InAs quantum dots embedded in a high electron mobility transistor-like modulation doped structure and utilize lateral electron transport. A peak response of the QDIP appeared at λ=10.5 µm at T=80 K. We also found that the device exhibits bias-dependent responsivity.

All of the noise parameters of a GaAs metal-semiconductor field-fffect transistor (MESFET) are extracted using 2-dimensional Monte-Carlo simulation for the first time. The general procedure for extracting the noise parameters is presented. The spectrums and correlations of the input-equivalent noise-voltage and noise-current sources are calculated. The y parameters of a GaAs MESFET are also extracted to obtain noise parameters and to analyze device characteristics for the first time.

Quasi-two-dimensional hole gas in strained Si/SixGe1-x /Si quantum well structure is investigated both theoretically and experimentally. The hole effective mass and the charge distribution in the structure are obtained from the self-consistent solution of the Schr\ddotodinger-Poisson equations. The calculation results show the dependence of the averaged mass on the measurement temperature and the averaged mass of 0.20 m 0 at T = 4 K. High quality Si/Si0.8Ge0.2/Si p-type modulation-doped quantum well is grown by molecular beam epitaxy and the electrical properties measured. Hall mobility as high as ∼10,400 cm2/V·s with a sheet carrier concentration of ∼1.1 ×1012 cm-2 and an effective mass of ∼0.30 m 0 is obtained at T = 4 K.

A new GaAs field effect transistor (FET) with dipole-barrier (DIBFET) employing a delta-n (δ n ) layer and a delta-p (δ p ) layer is proposed and fabricated. Electrons are confined in the upper undoped-GaAs layer (the channel layer) rather than around the δ n layer by the influence of the transverse electric field resulting from the dipole-barrier formation. This leads to the high electron concentration of 1.5×1018 cm-3 with the electron drift mobility of 3600 cm2/V·s in the undoped GaAs channel at room temperature. The fabricated GaAs DIBFET with 0.8 µm gate length shows the maximum value of extrinsic transconductance of 366 mS/mm. The drain current density is larger than 800 mA/mm. The current gain cutoff frequency f T of 16.7 GHz and the maximum oscillation frequency f max of 67 GHz are obtained. One-dimensional calculation of device characteristics is performed for the purpose of evaluating the device performance.