Kansho Yamamoto

High-frequency lamb wave device composed of MEMS structure using LiNbO 3 thin film and air gap

High-frequency devices operating at 3 GHz or higher are required, for instance, for future 4th generation mobile phone systems in Japan. Using a substrate with a high acoustic velocity is one method to realize a high-frequency acoustic or elastic device. A Lamb wave has a high velocity when the substrate thickness is thin. To realize a high-frequency device operating at 3 GHz or higher using a Lamb wave, a very thin (less than 0.5 μm thick) single-crystal plate must be used. It is difficult to fabricate such a very thin single crystal plate. The authors have attempted to use a c-axis orientated epitaxial LiNbO3 thin film deposited by a chemical vapor deposition system (CVD) instead of using a thin LiNbO3 single crystal plate. Lamb wave resonators composed of a interdigital transducer (IDT)/the LiNbO3 film/air gap/base substrate structure like micro-electromechanical system (MEMS) transducers were fabricated. These resonators have shown a high frequency of 4.5 and 6.3 GHz, which correspond to very high acoustic velocities of 14 000 and 12 500 m/s, respectively, have excellent characteristics such as a ratio of resonant and antiresonant impedance of 52 and 38 dB and a wide band of 7.2% and 3.7%, respectively, and do not have spurious responses caused by the 0th modes of shear horizontal (SH0) and symmetric (S0) modes.

High-Frequency Lamb Wave Device Composed of LiNbO3 Thin Film

The Lamb wave type of high frequency resonator was proposed. But any Lamb wave resonator operating really above 3 GHz, which is difficult to be realized with conventional surface acoustic wave (SAW), have been not reported. Authors have tried to realize the high frequency device by using A1 mode of Lamb wave propagating in the X-axis direction on Z-cut thin LiNbO3 film deposited by chemical vapor deposition system (CVD) having high velocity and high electromechanical coupling factor. As the result, authors have realized a 4.5 GHz high frequency Lamb wave resonator with high velocity of 14,000 m/s, large impedance ratio of 52 dB, and wide bandwidth of 7.2 % composed of thin LiNbO3 epitaxial film/air-gap/substrate for the first time. Also it is found that the thin LiNbO3 film is twined crystal. It is confirmed theoretically and experimentally that the spurious responses such as SH0 mode can not be excited because of twined crystal effect.

High frequency Lamb wave device composed of LiNbO 3 thin film

The Lamb wave type of high frequency resonator was proposed. But any Lamb wave resonator operating really above 3 GHz, which is difficult to be realized with conventional surface acoustic wave (SAW), have been not reported. Authors have tried to realize the high frequency device by using A1 mode of Lamb wave propagating in the X-axis direction on Z-cut thin LiNbO3 film deposited by chemical vapor deposition system (CVD) having high velocity and high electromechanical coupling factor. As the result, authors have realized a 4.5 GHz high frequency Lamb wave resonator with high velocity of 14,000 m/s, large impedance ratio of 52 dB, and wide bandwidth of 7.2 % composed of thin LiNbO3 epitaxial film/air-gap/substrate for the first time. Also it is found that the thin LiNbO3 film is twined crystal. It is confirmed theoretically and experimentally that the spurious responses such as SH0 mode can not be excited because of twined crystal effect.

Pyroelectric aluminum nitride micro electromechanical systems infrared sensor with wavelength-selective infrared absorber

This paper describes a micro electromechanical systems type wavelength-selective pyroelectric sensor, with highly c-axis oriented Aluminum nitride film as the pyroelectric material. Wavelength-selective infrared absorption is realized via periodic structures of holes patterned into the top metal electrode that also collects pyroelectric charge signal. The periodic hole array results in optical absorption resonances whose wavelength is determined by the hole pitch, demonstrated experimentally using a Fourier transform infrared spectrometer and numerically calculated using the finite difference time domain method. A significant difference in infrared absorption between patterned and unpatterned detectors is demonstrated through optical experiments comparing the pyroelectric responses.

Acoustic Wave Devices Composed of Periodically Poled Z -Cut LiTaO3 Plate Using Edge Reflection

The excitation method using the periodically poled (PP) structure has several merits suited for high-frequency devices in comparison with the excitation method using a conventional interdigital transducer (IDT). For example, a simple photolithography process, absence of short circuit caused by metallic powder, and a strong electric power durability can be expected. Although transducers using PP plates or PP films have been reported, none of the resonator-type devices using them has been. The authors attempted to fabricate PP resonators and resonator filters by applying an edge reflector to the fabrication of PP structure devices. As the result, a resonator having an impedance ratio of 33 dB and a resonator filter having an insertion loss of 2.6 dB and a relative 3 dB bandwidth of 2.2% were realized.

Acoustic wave devices using periodical poled Z-cut LiTaO 3 plate

Though acoustic wave devices using a periodical poled Pb(Zix, Ti1−x)O3 (PZT) ceramic plate on Si substrate, a periodical poled Pb(Zr0.2Ti0.8)O3 thin film on (001)SrTiO3 substrate, and a periodical poled Z-LiNbO3 substrate have been reported, their frequency responses were very weak as 0.1 to 3dB. It is considered that because their periodical poled devices have neither electrode fingers of intergidital transducers (IDTs) nor grating electrode reflectors, they do not have any effective reflection to realize a good frequency response, while conventional SAW devices have them. This time, authors have proposed an effective reflector for the periodical poled substrate device and applied it to a resonator and a resonator filter using a periodical poled Z-plane LiTaO3 plate, which is different from previously reported substrates. As the result, authors realized the resonator and the resonator filter having good frequency characteristics such as an impedance ratio of 33dB, and an insertion loss of 2.6 dB and a relative bandwidth of 2.2 %, respectively, for the first time.

Experimentally validated aluminum nitride based pressure, temperature and 3-axis acceleration sensors integrated on a single chip

This paper reports a unified fabrication process used to build multiple Aluminum Nitride (AlN) based micro-electromechanical system (MEMS) sensors on a single chip. A fully functional AlN-based sensor cluster has been demonstrated and is presented in this paper. This sensor cluster is a “five degree-of-freedom” cluster; it measures 3-axis acceleration, temperature and pressure fabricated on a 1 cm × 1 cm die. In addition to utilizing AlN as both the structural and active layer of the sensors, this work is novel because all sensors are fabricated in the same fabrication run.

High frequency lamb wave resonator using LiNbO 3 thin film by CVD

It has been considered that it is difficult to realize higher frequency devices than 3 GHz by using conventional surface acoustic wave (SAW) substrate. In order to realize a high frequency device, there are some methods such as using a high velocity substrate or shortening a wavelength (λ) of an interdigital transducer (IDT). However, almost of all conventional SAW substrates have a low velocity and it is difficult to shorten the λ of IDT because of too narrow fingers. A Lamb wave has a high velocity and a large coupling factor when a LiNbO3 plate is thiner than 0.2λ. As it is difficult to realize a very thin LiNbO3 crystal plate, author use a thin epitaxial LiNbO3 film deposited by a chemical vapor deposition (CVD). As the result, authors realized a high frequency 4.5 GHz of Lamb wave resonator composed of an electrode/thin epitaxial LiNbO3 film/air gap/base-substrate for the first time. The resonator showed a high velocity of 14,000 m/s, a large impedance ratio of 52 dB, and a wide bandwidth of 7.2 % without spurious response due to SH0 mode.

Preparation of (K, Na)NbO 3 -CaTiO 3 film by RF magnetron sputtering

Lead-free piezoelectric (K, Na)NbO₃-CaTiO₃ (KNN-CT) films were prepared on Pt/Ti/SiO₂/Si substrates by RF magnetron sputtering. Co-sputtering using a number of KNN-CT targets which vary in compositions of Na/(K+Na) ratio and amount of CaTiO₃ provided variations in compositions of KNN-CT films. The obtained KNN-CT films had compositions corresponding to the average compositions of the used targets represented by chemical formula of (1-n)(K_1-x, Na_x)NbO₃-nCaTiO₃ (x=0.460-0.617, n=0.000-0.065) and the compositional dependencies of their piezoelectric properties were studied. Most KNN-CT films with n>0.000 exhibited relatively high transverse piezoelectric coefficients |e₃₁ *|=|d₃₁|/s_11,p>6.0C/m² (where s_11,p is elastic compliance of the KNN-CT films), whereas n=0.000 |e₃₁ *|<;5.0C/m². In XRD analysis, (002) peak angle of these pseudocubic perovskite films increased with increase of n. From these results, we conclude that CaTiO₃ was successfully substituted as part of KNN and piezoelectric constant increased by effect of CaTiO₃. In addition, the KNN-CT films with x=0.587-0.617 and n=0.027-0.053 exhibited higher |e₃₁ *| than any other x and n. Moreover, by 750°C post-annealing process, |e₃₁ *| of the KNN-CT film with x=0.587 and n=0.040 was enhanced and the highest |e₃₁ *|=11.7C/m² was confirmed. This result of our experiment shows one of highest piezoelectric coefficient for lead free piezoelectric films.

4.5 GHz Lamb wave device composed of LiNbO 3 thin film

A high frequency device of 3 GHz or more is required, for instance, for future 4-th generation mobile phone system in Japan. Using a substrate with a high velocity is one method to realize a high frequency elastic device. A Lamb wave has a high velocity when the substrate thickness normalized by a wavelength (λ) of an elastic wave is thin. It is difficult to make a very thin crystal plate in order to realize a high frequency device. The authors have attempted to fabricate a Lamb wave device using a c-axis orientated thin LiNbO3 film deposited by a chemical vapor deposition system (CVD). A Lamb wave resonator composed of a interdigital transducer (IDT)/thin LiNbO3 film/air gap/base substrate has shown a high frequency of 4.5GHz, which corresponds a high velocity of 14,000m/s, and an excellent characteristics such as an impedance ratio of 52 dB and a wide band of 7.2%.