Hideharu Ieki

Quasi-microwave band longitudinally coupled surface acoustic wave resonator filters using ZnO/sapphire substrate

The 1.5 and 2.4 GHz range 5IDT-type longitudinally coupled surface acoustic wave (SAW) resonator filters have been developed using ZnO/sapphire substrate. The 1.5 GHz range SAW filter has the minimum insertion loss of 1.0 dB and the relative bandwidth of 2.4% at the insertion loss of 3 dB. The 2.4 GHz range SAW filter has the minimum insertion loss of 1.7 dB and the relative bandwidth of 1.7% at the insertion loss of 3 dB. These filters are suitable for use as RF-stage filters in a personal digital cellular (PDC) system terminal and a wireless local area network (LAN) adapter, respectively.

Microwave low insertion loss SAW filter by using ZnO/sapphire substrate with Ni dopant

Microwave low insertion loss SAW filters are realized by using ZnO epitaxial films on a sapphire substrate. The epitaxial growth conditions and dopant are carefully determined to realize low propagation loss and high stability. 1.5 to 2.5 GHz range SAW filters are fabricated with an insertion loss of only 1 to 2 dB and outline dimensions of 0.01 to 0.02 cc.

Monolithic oxide–metal composite thermoelectric generators for energy harvesting

Monolithic oxide–metal composite thermoelectric generators (TEGs) were fabricated using multilayer co-fired ceramic technology. These devices consisted of Ni0.9Mo0.1 and La0.035Sr0.965TiO3 as p- and n-type thermoelectric materials, and Y0.03Zr0.97O2 was used as an insulator, sandwiched between p- and n-type layers. To co-fire dissimilar materials, p-type layers contained 20 wt. % La0.035Sr0.965TiO3; thus, these were oxide–metal composite layers. The fabricated device had 50 pairs of p–i–n junctions of 5.9 mm × 7.0 mm × 2.6 mm. The calculated maximum value of the electric power output from the device was 450 mW/cm2 at ΔT = 360 K. Furthermore, this device generated 100 μW at ΔT = 10 K and operated a radio frequency (RF) transmitter circuit module assumed to be a sensor network system.

Epitaxially grown Al electrodes for high-power surface acoustic wave devices

A deposition process of epitaxial Al film on a quartz substrate was studied to obtain Al electrodes of surface acoustic wave (SAW) devices having high resistance to stress migration. A vapor deposition system was used under relatively moderate deposition conditions: (1) pressure range of 10 −5 Pa; (2) deposition temperature of 150°C; (3) deposition rate in the range of 120∼240 nm/min. The growth mode of epitaxial Al film differed from that of polycrystalline Al film on quartz

1.86 GHz SAW Filter

Using the third order harmonic wave of Sezawa-mode which propagates in ZnO films epitaxially deposited on R-plane sapphire, high performance filter which is a low insertion loss of 9 dB at 1.86 GHz has been realized.

Degradation of potential barriers in ZnO-based chip varistors due to electrostatic discharge

Degradation of potential barriers in ZnO-based varistors due to the electrostatic discharge (ESD) was investigated using scanning probe microanalysis and capacitance-time and isothermal capacitance transient spectroscopies. Pr6O11-ZnO (Pr-ZnO) varistors exhibit excellent ESD withstand capability compared with Bi2O3-ZnO (Bi-ZnO) varistors. After the application of ESD, asymmetrically degraded double Schottky barriers were observed in both Pr-ZnO and Bi-ZnO varistors, and the Schottky barrier in Bi-ZnO was found to be destroyed. The potential barriers of both types of varistors can respond to an ESD pulse, whose rise time is ∼1 ns, but after application of the ESD pulse, the Bi-ZnO varistor takes more time to recover its initial capacitance than does the Pr-ZnO varistor. Such difference in the transient behaviors of potential barriers is attributed to differences in the energy and distribution of interfacial states of Pr-ZnO and Bi-ZnO varistors. Experimental results clearly indicated a strong correlation b...

SAW Resonators Using Epitaxially Grown Al Electrodes

Epitaxially grown Al electrode was obtained on rotated Y cut quartz substrate by vapor deposition. The epitaxial relationship was (311) Al//(032) SiO2. This electrode had very high resistance to stress migration. In SAW resonators, time to failure caused by stress migration was improved by more than 2000 times and power handling capability was increased by at least 10 times over an ordinary polycrystalline Al–Cu electrode. Epitaxially grown Al electrode was also obtained on LST-cut quartz substrate.

Impact of the Electrical Forming Process on the Resistance Switching Behaviors in Lanthanum-Doped Strontium Titanate Ceramic Chip Devices

The resistance switching (RS) behaviors of La-doped SrTiO3 ceramics before and after the electrical forming process (E-forming) have been investigated in order to clarify the RS mechanism. The formation processes for the double Schottky barriers (DSBs), such as reoxidation and E-forming, are important to realize stable RS properties, and Joule heating strongly influences the RS behaviors after the E-forming. Thermally stimulated current measurements clearly indicated the contribution of defects related to oxygen vacancies to the current conduction through DSBs and RS phenomena both before and after the E-forming. Experimental results suggest that the electron trapping in the defects and/or the defect migration induced by the voltage application and Joule heating change the space-charge distribution near the grain boundaries, resulting in the change in the resistance state.

Piezoelectric, Dielectric, and Structural Properties of Ternary (K0.5Na0.5)Nb0.95O3–BaTiO3–BaZrO3 Thin Films Prepared on Pt/TiOx/SiO2/Si Substrates by the Chemical Solution Deposition Method

Well-controlled polycrystalline (1-x-y)(K0.5Na0.5)Nb0.95O3–xBaTiO3–yBaZrO3 (KNN–BTO–BZO; 0≤x,y ≤0.1) thin films were systematically synthesized on Pt/TiOx/SiO2/Si substrates by the chemical solution deposition (CSD) method in order to improve the piezoelectric properties by the formation of the morphotropic phase boundary (MPB). The synthesized thin films exhibited excellent insulated resistance and ferroelectric properties. Experimental results indicated that the tetragonal structure was fabricated in the range of at least 0.05≤x ≤0.1 in (1-x)KNN–xBTO, whereas the rhombohedral structure was not formed at room temperature in the range of 0≤y ≤0.1 in (1-y)KNN–yBZO thin films. Therefore, the desired MPB between tetragonal and rhombohedral structures was not formed in the fabricated KNN–BTO–BZO thin films, which hinders the improvement in the piezoelectric property of d33* from that of (K0.5Na0.5)Nb0.95O3. This finding demonstrates that the original composition control with the consideration of the effects of the strain from substrate and the small grain size is indispensable for further improvement in the piezoelectric properties of KNN thin films.