IEEE Standard on Piezoelectricity has been utilized for decades though it has shown significant issues that prevent researchers from obtaining accurate materials coefficients. To resolve these issues, our research group recently proposed partial electrode (PE) method. PE method utilizes samples that consist of the center part covered with electrode, and the side part either covered or not covered with electrode for obtaining both intensive and extensive elastic parameters. In this review, we introduce our PE method, along with physical phenomenology and background, such as issues of IEEE standard, to bolster readers understanding of needs for developing new measurement method that can compensate the standard method. It is shown that development of the PE method not only provides technological benefits, but also gives scientific importance for the piezoelectric research community from its extremely high data accuracy.

In this study, functional transparent conducting layers were investigated for Si-based photoelectric applications. Double transparent conductive oxide (TCO) films were deposited on a Si substrate in the sequence of indium tin oxide (ITO) followed by aluminum-doped zinc oxide (AZO). First, we observed that the conductivity and transparency of AZO dominate the overall performance of the double TCO layers. Secondly, the double layered TCO film (consisting of AZO/ITO) deposited by sputtering was compared to a AZO-only film in terms of their optical and electrical properties. We prepared three different AZO films: ITO:3min/AZO:10min, ITO:5min/AZO:7min, and ITO:7min/AZO:4min. The results show that the optical properties (transmittance, absorbance, and reflection) can be controlled by the film composition. This may provide a significant pathway for the manipulation of the optical and electrical properties of photoelectric devices.

Lead zirconate titanate/poly-vinylidene fluoride (PZT/PVDF) piezoelectric devices were fabricated by incorporating carbon nanotubes (CNTs), for use as flexible energy harvesting devices. CNTs were added to maximize the formation of the β phase of PVDF to enhance the piezoelectricity of the devices. The phase transition of PVDF induced by the addition of CNTs was confirmed by analyzing the X-ray diffraction patterns, scanning electron microscopy images, and atomic force microscopy images. The enhanced output efficiency of the PZT/PVDF piezoelectric devices was confirmed by measuring the output current and voltage of the fabricated devices. The maximum output current and voltage of the PZT/PVDF piezoelectric devices was 200 nA and 350 mV, respectively, upon incorporation of 0.06 wt% CNTs.

A high-performing photoelectric device was realized for the MoS₂-embedded Si device. MoS₂-coating was performed by an available large-scale sputtering method. The MoS₂-layer coating on the p-Si spontaneously provides the rectifying current flow with a significant rectifying ratio of 617. Moreover, the highly optical transmittance of the MoS₂-layer provides over 80% transmittance for broad wavelengths. The MoS₂-embedded Si photodetector shows the sensitive photo-response for middle and long-wavelength photons due to the functional MoS₂-layer, which resolves the conventional limit of Si for long wavelength detection. The functional design of MoS₂-layer would provide a promising route for enhanced photoelectric devices, including photovoltaic cells and photodetectors.

NiO serves as a window layer for Si photoelectric devices. Due to the wide energy bandgap of NiO, high optical transparency (over 80%) was achieved and applied for Si photoelectric devices. Due to the high the high mobility, the heterojunction device (Al/n-Si/SiO2/p-NiO/ITO) provide ultimately fast photoresponses of rising time of 38.33 μs and falling time of 39.25 μs, respectively. This functional NiO layer would provide benefits for high-performing photoelectric devices, including photodetectors and solar cells.

Highly optical transparent photoelectric devices were realized by using a transparent metal-oxide semiconductor heterojunction of p-type NiO and n-type ZnO. A functional template of ITO nanowires (NWs) was applied to this transparent heterojunction device to enlarge the light-reactive surface. The ITO NWs/n-ZnO/p-NiO heterojunction device provided a significant high rectification ratio of 275 with a considerably low reverse saturation current of 0.2 nA. The optical transparency was about 80% for visible wavelengths, however showed an excellent blocking UV light. The nanostructured transparent heterojunction devices were applied for UV photodetectors to show ultra fast photoresponses with a rise time of 8.3 mS and a fall time of 20 ms, respectively. We suggest this transparent and super-performing UV responser can practically applied in transparent electronics and smart window applications.

In this study, in order to develop coupled vibration mode piezoelectric devices for Acoustic Emission(abbreviated as AE) sensor application with outstanding displacement and piezoelectric properties have been simulatedby ATILA FEM program. And, From the results of ATILA simulation, the AE sensor specimen, obtained superiorelectromechanical coupling factor and displacement, when the size of specimen is 3.45 mmΦ×3.45 mm with ratio ofdiameter/thickness(Φ/T)= 1.0. Therefore, AE sensor was fabricated by (Na,K,Li)(Nb,Ta) O3(abbreviated as NKL-NT)system piezoelectric ceramics using coupled vibration mode. The piezoelectric properties of NKL-NT ceramics wasexhibited that piezoelectric constant(d33), piezoelectric voltage constant(g33) and electro mechanical coupling factor(kp)have the excellent values of 261[pC/N], 40.10[10-3Vm/N], and 0.44, respectively. The manufactured piezoelectric devicewith ratio of Φ/T= 1.0 indicated the optimum values of resonant frequency(fr)= 556.5[kHz], antiresonant frequency(fa)=631.1[kHz], and effective electromechanical coupling factor(keff)= 0.473. The maximum sensitivity of the coupledvibration mode AE sensor was 55[dB] at the resonant frequency of 75[kHz]. The results show that the coupledvibration mode piezoelectric device is a promising candidate for the application AE sensor piezoelectric device.

A thin metal-embedding Schottky device was fabricated for an efficient photoelectric device. Semitransparent thick of 10 nm metal layers were deposited by sputtering of Ag and Ni on a Sisubstrate. The (111) N-type Si wafers with one-side polished, 450∼500 ㎛ and resistivity 1∼20 Ω·㎝were used. High rectifying ratio about 100 from Ni-Schottky device was achieved. This design wouldprovide an effective scheme for high-performing photoelectric devices.

In this study, coupled mode piezoelectric devices for AE sensor application with excellent displacement and piezoelectric characteristics were simulated using ATILA FEM program, and then fabricated. Displacements and electromechanical coupling factors of the piezoelectric devices were investigated. The simulation results showed that excellent displacement and electromechanical coupling factor were obtained when the ratio of diameter/thickness was 1.0. The piezoelectric device of ф/T= 1.0 exhibited the optimum values of fr= 406 kHz, displacement= 6.11 × 10^-8[m], k_eff= 0.648. The results show that the coupled vibration mode piezoelectric device is a promising candidate for the application of AE sensor piezoelectric device.

In this study, thickness vibration mode piezoelectric devices for AE sensor application were simulated using ATILA FEM program, and then fabricated. Trajectory resonant displacement and electro mechanical coupling factors of the piezoelectric devices were investigated. The simulation results showed that excellent displacement and electro mechanical coupling factor was obtained when the ratio of diameter/thickness(Ф/T) was 0.75. The piezoelectric device of Ф/T=0.75 exhibited the optimum values of fr=183 kHz, displacement=4.44×10(-7)[m], k33=0.69, which were suitable for the application of AE sensor piezoelectric device.