第39回「センサ・マイクロマシンと応用システム」シンポジウム（以下，センサシンポジウム）は，2022年11月14日（月）～16日（水）に「アスティとくしま」にて，テクニカルツアーは11月17日（木）に開催された。

第39回となった本センサシンポジウムは，基調講演3

This paper addresses a pressure sensor for body pressure measurement. Many pressure sensors have been developed for disease treatment in the medical field. However, these sensors require inserting electronic components and other sensor elements via surgical operations, so the measurement physically burdens patients. Hence, we proposed a needle-type pressure sensor using MEMS (Micro Electro Mechanical Systems) cantilever. The sensor has a needle part with a thin membrane on the tip and is filled with incompressible fluid inside. The fractional resistance of the built-in piezoresistive cantilever varies according to the pressure change applied to the needle tip. We can measure body fluid pressure with minimal surgery by inserting a simple needle into the target organ. Because the fabricated sensor responded to pseudo-body pressure changes, it was suggested that the fabricated needle-type pressure sensor could detect pressure inside the body.

In this paper, we have proposed a semicircular curved hetero-core optical fiber accelerometer consisting of an optical fiber and a mass for low-frequency vibration monitoring. Experimental results showed that the proposed accelerometer with the mass installed had improved sensitivity in the low-frequency range and that differences in sensitivity occurred depending on the direction of the applied vibration. Sensitivities in the direction of in-plane shear deformation were 4.4×10^-1, 1.3×10^-1, and 8.1×10^-3 dB/g with 2×10^-4 kg, 7×10^-5 kg, and without mass, respectively. Experimental results showed that heavier mass improved sensitivity in the low-frequency range. Besides, the sensitivity in the out-of-plane bending deformation direction was lower than that in the in-plane shear deformation direction, with a transverse sensitivity of 15 to 25% compared with the in-plane shear deformation sensitivity. In addition, the frequency response characteristics obtained from the FE analysis and experiments revealed a trade-off between sensitivity and measurable frequency range depending on the mass condition.

We have developed tactile sensor systems for next-generation robots. To install a large number of tactile sensors, we have proposed MEMS-LSI integrated tactile sensors. The integrated device has following features: capacitive type 3-axis force sensing, embedded diode-based temperature sensing, signal processing for sensing data digitalization, and event-driven response for efficient serial bus communication. This paper demonstrates a sensor array system as up-to 40 integrated tactile sensors which are connected on one bus line. After acquiring the sensing data from the sensor array system, we applied a machine learning technique for target object judgment. The objective of the judgment is to classify the targets into normal object and abnormal object. With the sensor array system, data preprocessing and tuned RNN/LSTM neural network models, we achieved high-accuracy, high-precision, and high-recall scores for the experiment of the judgment.

This paper introduces a Photoacoustic Spectroscopy (PAS) sensor using a highly sensitive pressure sensor composed of silicon piezoresistive cantilever for continuous non-invasive measurement of blood glucose. By measuring photoacoustic waves generated by far-infrared light with the silicon piezoresistive cantilever, the sensor can measure the photoacoustic waves without resonator. This enables to miniaturize the sensor size. The minimum resolution of the silicon piezoresistive cantilever was about 10 µPa, and we confirmed that the prototype PAS sensor can be used to measure 60 mg/dL density glucose in liquid.

Nanopore-based sensing methods are valuable tools for solution-based single-particle analysis of many biomolecules and particles that play important roles in life and medicine, such as nucleic acids, proteins, viruses, and exosomes. The conventional nanopore method is based on direct current measurement, and the available information on particle size and zeta potential is limited. Here, we developed an alternating current-based nanopore method using lock-in measurement to overcome the longstanding and conflicting limitations of both low noise and wide bandwidth, thereby demonstrating impedance measurement of a single nanoparticle. We determined the particle size, zeta potential, and electric capacitance from the frequency responses of various particles ranging in diameter from 100 nm to several micrometers. Our nanopore method was highly accurate, identifying the type of virus with over 85% sensitivity using single-particle measurement and machine learning. This method is expected to have a variety of applications such as sensing of various nanoparticles and characterization of single nanoparticles.

In order to clarify an effect of core-shell structuring on the thermoelectric properties of silicon nanowires (SiNWs), a new evaluation device with monolithic integration of bottom-up-grown SiNWs was developed, and Al₂O₃-shell-coated p-type SiNWs were evaluated. In fabrication, SiNWs bridge structures were successfully formed with a high yield of 61% on desired local region, by employing VLS processes combined with surface nanoholes formation. Evaluated resistivity and Seebeck coefficient of the core-shell SiNW bridges were 7.6 Ω·cm and 0.61 mV/K, respectively. The Seebeck coefficient was compared with those of p-type bulk and nano Si structures to discuss effect of core-shell structuring.

We propose a fabrication method of optical fiber bundles with wire-grid polarizers (WGPs) on the end face and its applicability to the discrimination between healthy and decalcified tooth substances in dental care. A chip with WGPs formed in accordance with the core arrangement was fabricated and attached to the end face of an optical fiber bundle while being aligned. The transmittance and polarization extinction ratio of WGPs were evaluated by illuminating the end face of the optical fiber bundle through a rotational polarizer. The diffuse reflectance spectra of tooth substances were evaluated using a microspectroscopic system and the optical fiber bundle with WGPs. The results confirmed that the tooth substances could be discriminated from the light intensities at wavelengths of 450 nm and 1500 nm.

We developed a body-conduction microphone prototype to monitor the scratching intensity in dogs. Reliable monitoring of the scratching intensity is required to promote the well-being of dogs. This can lead to early detection of dermatoses and reduce stress and discomfort. To sense body-conducted scratching sounds using a dog’s collar, we developed a prototype body-conduction microphone. The performance of our sensor to estimate scratching intensity was compared to conventional accelerometer data. As a result, our sensor and the accelerometer estimated scratching intensity with a correlation coefficient of 0.66 and 0.089, respectively, under the body motion noise.

In this paper, our room-temperature bonding method using activated Si atomic layer demonstrated wafer-level hetero integration of thin film LiNbO₃ on insulator (LNOI) electro-optical modulator arrays on Si. The integration of LNOI photonics with Si, which is a promising platform for LSI, MEMS, and Si photonics, is expected to produce highly functional and multi-functional opto-electro-mechanical platforms.

This paper describes lift-off process for 1 µm fine pattern using single layer lift-off photoresist. For the lift-off process, tapered structure or undercut structure of single layer photoresist was achieved by selecting appropriate photoresist and adjusting exposure dose and development time of photolithography. Then we deposited 0.3 µm-thick aluminum by electron beam evaporator. In order to make aluminum particles reach the patterned substrate perpendicularly, we used the fixed stage instead of the planetary rotating stage. As the result, we successfully fabricated 1 µm 1:1 line and space, 0.3 µm-thick Al pattern using single layer photoresist.