Chul An

The design of a temperature-stable stepped-impedance resonator using composite ceramic materials

The authors present a method to design a coaxial ceramic resonator, whose resonance frequency is unchanged with temperature, using a material with a positive temperature coefficient of resonant frequency (/spl tau//sub f/) and a negative /spl tau//sub f/ material. From the resonance conditions according to temperature variation, the length to be filled with each material is calculated to minimize the resonance frequency shift with temperature change. As an example, Ba(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/ and CaZrO/sub 3/ are selected in this work, and their lengths are obtained at various resonant frequencies. The temperature dependence of the resonant frequency of this resonator is simulated.

The microwave dielectric properties of xTiO2(1−x)CeO2 ceramics

The xTiO2(1−x)CeO2 system was investigated and its dielectric properties were measured. In order to achieve a temperature-stable material, we studied a method of combining a positive temperature coefficient material with a negative one. CeO2 was measured to have dielectric constant er=24, Q*f=57,000 and τf=−104 ppm/°C. TiO2 has er=93, Q*f=10,000 and τf=350 ppm/°C. xTiO2(1−x)CeO2 system has the dielectric properties as follows: 32<er<74, 25,000<Q*f<43,000 and −100<τf<300. It is the temperature-stable material that is achieved. A series of new xTiO2(1−x)CeO2 dielectric materials were synthesized. Its dielectric characteristics(er, Q*f and τf) are intermediate between TiO2 and CeO2. It is found that the ceramic in the xTiO2(1−x)CeO2 system has excellent dielectric characteristics at microwave frequencies.

Microwave dielectric properties of xMgTiO3-(1 − x)(Na1/2Ln1/2)TiO3 ceramics

Na1/2Ln1/2)TiO3> ceramic has a high relative dielectric constant and a positive temperature coefficient of resonant frequency (τf) (where Ln represents a lanthanide: La+3, Pr+3, Nd+3 and Sm+3). On the other hand, MgTiO3 ceramic has a high Qf value and a negative temperature coefficient. We have investigated the microwave dielectric properties of MgTiO3-(1 − x)(Na1/2 Ln1/2) TiO3. In this system, there are no indications of a solid-solution or a secondary phase. There are mixed phases only with MgTiO3 and Na1/2 Ln1/2)TiO3 phases. Its dielectric characteristics (Q*f, temperature coefficient and dielectric constant) are intermediate between (Na1/2 Ln1/2) TiO3 and MgTiO3 and are predictable by the logarithmic mixing rule. The temperature coefficient of dielectric ceramic compositions approximates to zero at each Ln = La, x = 0.9, Ln = Pr, x = 0.87, and Ln = Nd, x = 0.84. At this time, there are Q*f values in the range of 55 000 to 28 000 GHz and relative dielectric constants in the range of 22 to 25.

Design and RF characteristics of traveling-wave electrodes for high-speed lithium niobate optical modulators

Various types of traveling-wave electrodes for a high-speed LiNbO/sub 3/ optical intensity modulator were fabricated and characterized from the viewpoints of the characteristic impedance, the effective refractive index and an attenuation constant, which were extracted from measurements in the time domain and the frequency domain. The effects of trenching the SiO/sub 2/ buffer layer on electrical properties were examined. In this work the maximum value of the optical 3 dB modulation bandwidth, calculated by experimental results, was 18 GHz, and it is suggested that optical/RF phase velocity matching and the impedance matching can be achieved, and thus a higher value of the optical 3 dB modulation bandwidth can be obtained.

Characteristics of a-si:h films prepared by ecr cvd as a function of the h2/sih4

The optical, electrical and structural properties of hydrogenated amorphous silicon films were investigated as a function of the H2/SiH4 ratio. The films were deposited by electron cyclotron resonance plasma chemical vapor deposition method in the source gas limited and electron flux limited mode. In the source gas limited mode, the properties of amorphous silicon films were improved with increasing deposition rate photoconductivity, hydrogen content increased and optical band gap, full width at half maximum of the Raman spectroscopy and the ratio of the concentration of dihydride to that of monohydride decreased. In the electron flux limited mode, the optical, electrical and structural properties as well as the deposition rate did not improved any more. The photoconductivity was over 10−5 Ω−1 cm−1 when the optical band gap was 1.75 ~ 1.77 eV, FWHM was below 75 cm−1, hydrogen content was about 21 at.% and the ratio of dihydride to the monohydride was about 1.5 in the electron flux limited mode.

Saturation of effective channel length increase due to hot carrier degradation in submicron LDD nMOSFETs

The effective channel length of submicron LDD nMOSFETs after hot carrier degradation was measured. After the hot carrier stressing, the effective channel lengths were increased with time but saturated after a certain threshold time of about 1000 s. The saturation nature of hot carrier degradation in LDD nMOSFETs can be understood through the saturation of the effective channel length.

Bipolar-Complementary-Metal-Oxide-Semiconductor (BiCMOS) Technology with Polysilicon Self-Aligned Bipolar Devices

An advanced bipolar-complementary-metal-oxide-semiconductor (BiCMOS) technology providing uncompromised high-performance, double polysilicon self-aligned (PSA) n-p-n bipolar and 1.25 µm gate length CMOS transistors is described. The polysilicon self-aligned-BiCMOS technology (PSA-BiCMOS) is intended for high-speed logic circuit operation at 5 V, where a high level of circuit integration and power consumption is involved. Features include vertical n-p-n transistors with a self-aligned n+ polysilicon emitter and p+ polysilicon base. The CMOS transistor features n+ polysilicon gates and lightly doped drain (LDD) NMOSFET. A process simulator, Stanford University process engineering models (SUPREM III) and device simulator, Poisson and continuity equation solver (PISCES II) were used to optimize the process steps and to enhance device characteristics, respectively. The performance of N- and PMOS transistors is comparable to those of a conventional CMOS process. The driving capability of CMOS and PSA-BiCMOS was compared according to fan-out. Compared to CMOS, PSA-BiCMOS has good driving capability from about 2.5 fan-out and PSA-BiCMOS with 1.25 µm N- and PMOS transistors and a bipolar transistor with 2 µm emitter width exhibits an average ring oscillator delay of 6.25 ns/stage at 1 pF load capacitance at 5 V.

Capacitance-Voltage Characteristics of SiO 2 Films Prepared by Electron Cyclotron Resonance Plasma Chemical Vapor Deposition as a Function of O 2 Content and Microwave Power

The capacitance-voltage characteristics of SiO2 films were investigated as a function of O2 content and microwave power using the electron cyclotron resonance plasma chemical vapor deposition method. The interface trap density was 1010~5×1011 eV-1cm-2. From the capacitance-voltage characteristics, we may assume that positive ions (O2+ or O+) exist in the SiO2 films and these positive ions increase with increasing O2 content or microwave power. Low ion energy is important for avoiding positive ions in oxide films so that high-quality oxide can be obtained.

The characteristics before and after annealing of amorphous silicon films prepared by ECR plasma CVD

Abstract The optical and electrical properties before and after annealing of amorphous silicon films, deposited by electron cyclotron resonance plasma chemical vapor deposition as a function of substrate temperature, were investigated. The properties of non-annealed Si films were improved with increasing substrate temperature. On the other hand, Hall mobility of annealed Si films decreased with increasing substrate temperature.

Improvement of sintering condition and dielectric characteristics of (Pb/sub x/Ca/sub 1-x/)ZrO/sub 3/ ceramics with addition of Pb(Fe/sub 2/3/W/sub 1/3/)O/sub 3/ ceramics

We report the effects of the addition of PFW on the decrease of the sintering temperature and the improvement of dielectric properties at microwave frequencies of the PCZ ceramic system. It was found that an addition of Pb(Fe/sub 2/3/W/sub 1/3/)O/sub 3/ promotes the grain growth, the solid solution between the Pb-based perovskite and the Ca-based perovskite and a decrease of the sintering temperature. We found that 0.05Pb(Fe/sub 2/3/W/sub 1/3/)O/sub 3/-0.95(Pb/sub x/Ca/sub 1-x/)ZrO/sub 3/ ceramic can be sintered at less than 1250/spl deg/C. The dielectric properties of this compound are better than those of the (Pb/sub x/Ca/sub 1-x/)ZrO/sub 3/ ceramic system.