Hidekuni Takao

Development of a disposable glucose biosensor using electroless-plated Au/Ni/copper low electrical resistance electrodes

This paper presents a glucose biosensor, which was developed using a Au/Ni/copper electrode. Until now, research regarding the low electrical resistance and uniformity of this biosensor electrode has not been conducted. Glucose oxidase (GOD) immobilized on the electrode effectively plays the role of an electron shuttle, and allows glucose to be detected at 0.055 V with a dramatically reduced resistance to easily oxidizable constituents. The Au/Ni/copper electrode has a low electrical resistance, which is less than 0.01 Omega, and it may be possible to mass produce the biosensor electrode with a uniform electrical resistance. The low electrical resistance has the advantage in that the redox peak occurs at a low applied potential. Using a low operating potential (0.055 V), the GOD/Au/Ni/copper structure creates a good sensitivity to detect glucose, and efficiently excludes interferences from common coexisting substances. The GOD/Au/Ni/copper sensor exhibits a relatively short response time (about 3s), and a sensitivity of 0.85 microA mM(-1) with a linear range of buffer to 33 mM of glucose. The sensor has excellent reproducibility with a correlation coefficient of 0.9989 (n=100 times) and a total non-linearity error of 3.17%.

An enhanced glucose biosensor using charge transfer techniques

An enhanced glucose biosensor based on a charge transfer technique glucose sensor (CTTGS) is described and demonstrated experimentally. In the proposed CTTGS, which is accumulation method (d-gluconate+H(+)) ion perception system, the quality of output signal with signal integration cycles is high. With the proposed CTTGS it is possible to amplify the sensing signals without an external amplifier by using an accumulation cycle. It can be supposed that measurements of small (d-gluconate+H(+)) ion fluctuation are difficult by ion-sensitive field effect transistor (ISFET) because the theoretical maximum sensitivity is only 59 mV/pH and the small output signals are buried in the 1/f noise component of the metal-insulator-semi-conductor field-effect transistor (MISFET). Therefore, the CTTGS has many advantages, such as high sensitivity, high accuracy, high signal-to-noise ratio (SNR), and has been successfully demonstrated using a charge transfer technique. The CTTGS exhibited excellent performance for glucose with a large span (1445 mV) and good reproducibility. Moreover, the CTTGS has good sensitivity in this range of 7.22mV/mM, a lower detection limit of about 0.01 mM/L and an upper detection limit of about 200 mM/L compared with amperometric glucose analysis which has been studied recently. Under optimum conditions, the proposed CTTGS exceeds the performance of the widely used ISFET glucose sensor. The sensitivity of the CTTGS (7.22 mV/mM) was seven times higher than that of the ISFET (1 mV/mM). Furthermore, the sensitivity obtained for human glucose levels was 29.06 mV/mM with a non-linear error of +/-0.27%; the linearity is y=0.0294x+1.8612 and R(2)=0.9999, which is acceptable for clinical application. Real sample analysis is investigated in blood glucose level by our developed CTTGS ISFET system.

Miniaturization of Electrical Conductivity Sensors for a Multimodal Smart Microchip

A new electrical conductivity (EC) sensor with Pt electrodes on a Si substrate was proposed for use in agricultural applications. The complementary metal oxide semiconductor (CMOS) logic technology-compatible sensor was successfully fabricated with a small chip (area, 25 mm2). This sensor was used for an alternating voltage, owing to the polarization of the Pt electrode and its best operation at 10 kHz frequency. Measurements were conducted on water with electrical conductivities ranging from 10-2 to 101 S/m, which shows sufficient linearity for use as a sensor for agriculture applications. It was also possible to be miniaturized. In an agricultural application, measurements were carried out with the sensor inserted in the rock wools, which was confirmed by the linearity of the values obtained using the sensor. In addition, successful real-time measurements using the sensor were conducted by inserting the sensor into the compost in the vicinity of the roots of a tomato seedling. This sensor provides a promising solution for an EC sensor for broad fields of agricultural applications.

Application of Silicon on Nothing Structure for Developing a Novel Capacitive Absolute Pressure Sensor

In the field of silicon on nothing (SON) structure , micrometer-thick monocrystalline layers suspended over their parent wafer were produced by high-temperature annealing of specific arrays of trenches. Those trenches reorganize into one single void and leave a thin overlayer on top. Since this method may be an easy way of synchronous fabricating high-quality silicon films and vacuum void, this paper investigates its potential applications for a pressure sensor. A capacitive absolute pressure sensor whose pressure sensitive membrane is formed by the SON structure was fabricated and evaluated. The radius and thickness of the sensitive membrane are 100 and 1.7-μm, respectively. The average sensitivity of the sensor array with 15 diaphragms is 2.88 fF/kPa. This novel fabrication process enables to easily form a high vacuum cavity without hermetical sealing process such as anodic bonding technology, to achieve an excellent long-term stability and reliability, in particular, and to easily integrate detection circuits with the sensor.

Oscillation-controlled CMOS ring oscillator for wireless sensor systems

This paper presents a ring oscillator with the function of the oscillation controlled for wireless sensor systems (WSSs). The proposed oscillator consists of a NAND gate, 4 inverters, and 1-, 3-, 9-times buffer stage. Operation of it is controlled by the NAND gate. The oscillator can reduce the power loss because the oscillator is oscillated during only high level input. The proposed oscillator was designed and fabricated by 2.5@mm CMOS technology, through which it is possible to realize a WSS on a single chip because a sensor and an oscillator can be fabricated concurrently. The frequency tuning range of the oscillator was found to be approximately 90-152MHz and the output power of the oscillator was -8.42dBm. The measured phase noise is -99.35 and -102.59dBc/Hz at 1 and 5MHz offsets, respectively, from the carrier of 152MHz. Power consumption of the oscillator is determined by the duty cycle of the input signal pulse, and the range of power consumption was measured as 1.5-45mW at the duty cycle of 1.0.

A Versatile Integration Technology of SOI-MEMS/CMOS Devices Using Microbridge Interconnection Structures

In this paper, a versatile integration technology for thick-film silicon-on-insulator microelectromechanical systems (SOI-MEMS) devices with CMOS electronics using novel microbridge interconnections is reported. The microbridge interconnection proposed in this paper solves the problem regarding the electrical isolation and interconnection between CMOS and SOI-MEMS devices. The integration of SOI-MEMS requires only three additional photolithography steps for the CMOS wafers fabricated by a standard process. On the basis of the developed technology, SOI-MEMS devices integrated with CMOS circuits were fabricated using 20-μm-thick SOI wafers. No significant damage was observed in the measured characteristics of the fabricated CMOS after the integration of MEMS devices. In addition, the electrical isolation of SOI-MEMS from the CMOS substrate was successfully realized and confirmed in the experiment, keeping electrical connectivity between CMOS circuit terminals. The measured isolation resistance between MEMS and the CMOS substrate was more than 1012 Ω, and a proof voltage above 60 Vdc was observed. These values guarantee a small leakage current and a sufficient voltage swing for driving electrostatic microactuators. On the other hand, the resistance of the interconnection over a microbridge structure was below 1 Ω, which is sufficiently low for integrating low-noise microsensors. This integration technology can be used in realizing monolithically integrated SOI-MEMS sensor and actuator devices with high-aspect-ratio structures using the most cost-effective and versatile CMOS fabrication technologies.

A membrane type Si-MEMS tactile imager with fingerprint structure for realization of slip sensing capability

This paper reports a newly developed Si-MEMS integrated tactile imager that can detect tri-axial input force and ‘slip’ on the surface of the sensor in high spatial resolution (several hundreds micron). Tactile imaging is performed by a large area silicon membrane which is integrating sensor pixel array including strain gauge circuits. The new imager device presented in this paper has fingerprint-like patterns formed by Deep-RIE on the silicon sensor diaphragm. The patterns generate a rotational motion for horizontal axis input force, and it is similar with the role of humans fingerprints. Basic principle of the tactile imager was examined with FEM analysis for multi-axis input forces and the slip sensing ability. In addition, tri-axial load was successfully detected in each pixel by the new membrane sensor structure with low cross-axis sensitivities.

Precise tumor size measurement under constant pressure by novel real-time micro-electro-mechanical-system hood for proper treatment (with videos).

BackgroundTumor size determination is subject to the measurement method used by endoscopists and is especially dependent on the air quantity. As the intraluminal pressure must be measured objectively to obtain an accurate tumor size measurement, insufflation can affect the results. Thus, we examined the utility of a micro-electro-mechanical-system (MEMS) pressure sensor hood.MethodsTwenty consecutive air insufflation/deflation tests were performed in vivo using a dog’s stomach. Correlations between the actual pressure measured and the signal strength of the MEMS hood were measured. We marked 2 points 20xa0mm on the antrum and another 3 points, with insufflation corresponding to the maximum stable distance of two markings. We performed five insufflation/deflation tests to obtain the relationship between pressure and distances to accurately measure the distance under constant pressure.ResultsIn the air insufflation/deflation test performed 20 consecutive times, the MEMS hood signal strength (V) and the pressure measurement sensor values (mmHg) showed good correlation. There was good correlation between intraluminal pressures of 2.5–40xa0mmHg and the two marking distances on the antrum (correlation coefficient 0.952) (Pxa0<xa00.05). However, once the intraluminal pressure reached a certain level (40xa0mmHg), expansion of the two marking distances ceased. The same measurements were conducted on the greater curvatures of the lower body and middle body and on the lesser curvature of the lower body.ConclusionsCorrect tumor size measurements using a MEMS hood enable a more accurate diagnosis, which can be used to develop suitable treatment strategies.

A novel integrated tactile image sensor for detection of surface friction and hardness using the reference plane structure

In this paper, a tactile sensor with detection abilities of hardness and friction of object surface is proposed and reported. The new detection principles of friction and hardness are realized with the reference plane structure on the device. The device was fabricated with LSI/MEMS integration technology. Completed the devices were evaluated, and the measured normal force sensitivity was 0.07mV/mN/V. On the other hand, the shear force sensitivity was 0.73mV/mN/V. This performance corresponds to the detection ability of frictional coefficient around 0.1. Also, shore A hardness was successfully measured in the range from 22 to 99 HS.

An Annular Mechanical Temperature Compensation Structure for Gas-Sealed Capacitive Pressure Sensor

A novel gas-sealed capacitive pressure sensor with a temperature compensation structure is reported. The pressure sensor is sealed by Au-Au diffusion bonding under a nitrogen ambient with a pressure of 100 kPa and integrated with a platinum resistor-based temperature sensor for human activity monitoring applications. The capacitance-pressure and capacitance-temperature characteristics of the gas-sealed capacitive pressure sensor without temperature compensation structure are calculated. It is found by simulation that a ring-shaped structure on the diaphragm of the pressure sensor can mechanically suppress the thermal expansion effect of the sealed gas in the cavity. Pressure sensors without/with temperature compensation structures are fabricated and measured. Through measured results, it is verified that the calculation model is accurate. Using the compensation structures with a 900 μm inner radius, the measured temperature coefficient is much reduced as compared to that of the pressure sensor without compensation. The sensitivities of the pressure sensor before and after compensation are almost the same in the pressure range from 80 kPa to 100 kPa.