Tetsu Fujii

Experimental demonstration for scanning near-field optical microscopy using a metal micro-slit probe at millimeter wavelengths

Scanning near-field optical microscopy using a slit-type probe is discussed. The slit-type probe has a width of much less than a wavelength, λ, and a length on the order of λ, and thus has high transmission efficiency. Two dimensional near-field images of objects have been constructed using an image reconstruction algorithm based on computerized tomographic imaging. Experiments performed at 60 GHz (λ=5 mm) show that this type of near-field microscopy can achieve a spatial resolution of better than λ/45 for two dimensional imaging. A method for fabricating a submicron width slit probe at the end of an optical fiber is presented for extending this microscopy to optical waves.

Colossal electroresistance effect at metal electrode/La1−xSr1+xMnO4 interfaces

We have studied the current-voltage (I-V) characteristics and resistance switching at the interface between metal electrodes M (=Pt, Au, Ag, Al, Ti, and Mg) and atomically flat cleaved (001) surfaces of La1−xSr1+xMnO4 (x=0–1.0) single crystals by using a three-probe method. Hysteretic I-V characteristics, indicating the appearance of the resistance switching, were observed in the junctions for M=Mg, Al, and Ti, which have relatively shallow work functions. The resistance switching ratio depends on the hole doping x and the optimal doping level is around x=0.5, verifying that the resistance switching property can be controlled by the doping level.

Fermi level shift in La1−xSrxMO3 (M=Mn, Fe, Co, and Ni) probed by Schottky-like heteroepitaxial junctions with SrTi0.99Nb0.01O3

The authors have studied electrical properties of perovskite heteroepitaxial junctions consisting of transition metal oxides La1−xSrxMO3 (LSMO: M=Mn, Fe, Co, and Ni) and an n-type semiconductor SrTi0.99Nb0.01O3 (Nb:STO). The junctions showed rectifying current-voltage characteristics that could be analyzed by taking into account a Schottky-like barrier formed in the Nb:STO at the interfaces. As the doping level x is increased, the Schottky barrier height and built-in potential increase as ∼x (eV), indicating the downward shift of the Fermi level position in the LSMO. The Fermi level position in the LSMO with the same doping level x tends to be deepened with increasing the atomic number of M, in the order of Mn, Fe, Co, and Ni.

An antenna switch MMIC using E/D mode p-HEMT for GSM/DCS/PCS/WCDMA bands application

A monolithic antenna switch IC using enhancement and depletion (E/D) - mode AlGaAs/InGaAs pseudomorphic high electron mobility transistors (p-HEMTs) has been developed for GSM/DCS/PCS/WCDMA band digital mobile communication systems. This antenna switch MMIC achieves a low insertion loss and small chip size using a single pole double throw (SPDT) switch for GSM and single pole 4 throw (SP4T) switch for other band configurations, as well as internal logic circuits with an E/D mode p-HEMTs process. This MMIC achieves an insertion loss of 0.21dB at 915MHz and 0.53dB at 1785MHz. The isolation to the RX ports is more than 30 dB, and the input power at 0.1 dB compression is over 36 dBm at +2.7 V operation.A monolithic antenna switch IC using enhancement and depletion (E/D) -mode AlGaAs/InGaAs pseudomorphic high electron mobility transistors (p-HEMTs) has been developed for GSM/DCS/PCS/WCDMA band digital mobile communication systems. This antenna switch MMIC achieves a low insertion loss and small chip size using a single pole double throw (SPDT) switch for GSM and single pole 4 throw (SP4T) switch for other band configurations, as well as internal logic circuits with an E/D mode p-HEMTs process. This MMIC achieves an insertion loss of 0.21 dB at 915 MHz and 0.53 dB at 1785 MHz. The isolation to the RX ports is more than 30 dB, and the input power at 0.1 dB compression is over 36 dBm at +2.7 V operation.

Spatial power combining of Gunn diodes using an overmoded waveguide resonator at millimeter wavelengths

An oscillator which incorporates an overmoded-waveguide resonator with an array of TE/sub 10/-mode waveguides containing Gunn diodes, has been developed as a means for achieving highly efficient spatial power combing. This oscillator makes use of mode conversion of radiation power from the Gunn diodes in the waveguide array to the overmoded-waveguide resonator, to produce high power at millimeter wavelengths. An efficiency of about 83% and an output power of 1.5 W (CW) at 61.4 GHz, has been achieved with a 3/spl times/3 waveguide Gunn diode array.

Coherent power combining of millimeter wave resonant tunneling diodes in a quasi-optical resonator

A Fabry-Perot resonator with a grating has been used for coherent power combining of a resonant tunneling diode (RTD) array in the millimeter wave region. Coherent power combining with two RTDs in the resonator has been successfully observed for the fundamental TEM/sub 00/ resonator mode at the frequency of 75 GHz.

An optically controlled modulator using a metal strip grating on a silicon plate for millimeter and submillimeter wavelengths

An optically controlled modulator using a metal strip grating on a silicon plate with an external electric field applied between the strips, has been developed as a quasi-optical high-speed modulator for millimeter and submillimeter wavelengths. The experimental results obtained at 52 GHz to 60 GHz show that the maximum modulation frequency in the inductive metal strip modulator can be increased from 4 kHz to 37 kHz by applying only 13 volts (E/spl sim/150 V/cm) to the strips. A higher modulation frequency is available for the metal strip modulator with a higher external electric field.