Hitoshi Yagi

A 160 x 120 pixel uncooled TEC-less infrared radiation focal plane array on a standard ceramic package

We have developed a 32 μm pitch and 160 × 120 pixel uncooled infrared radiation focal plane array (IRFPA) on SOI by 0.35 μm CMOS technology and bulk-micromachining. For IR detection, we use silicon single crystal series p-n junctions which can realize high uniformity of temperature coefficient and low voltage drift. We have also developed a low-noise CMOS readout circuit on the same SOI which can calibrate the substrate temperature variation in every frame period, comparing two types of pixels, a bulk-micromachined infrared detection pixel and a non-micromachined reference pixel. Then the FPA requires no thermo-electric cooler (TEC) and is mounted on a low-cost standard ceramic package for the consumer products market.

Rear-gate ISFET with a membrane locking structure using an ultrahigh concentration selective boron diffusion technique

Abstract A new rear-gate ISFET with a membrane locking structure has been developed in order to enhance mechanically the adhesion strength in the sensitive membrane. It is necessary to form a deeply diffused ultrahigh concentration region of boron in order to construct a well-shaped and mechanically strong locking structure using selective anisotropic wet etching. A novel selective boron diffusion technique characterized by patterning a liquid-type diffusion source has been investigated and optimum conditions have been obtained for the first time. Applying the conditions, a rear-gate ISFET with a sufficiently mechanically strong locking structure has been fabricated. The characteristics (fundamental FET characteristics, pH response and potassium ion response) of the new ISFET are satisfactory and it is confirmed that the sensor durability is imporved by adding the locking structure.

A SOI-based CMOS-MEMS IR image sensor with partially released reference pixels

We have developed a 22 µm pitch and 320 × 240 pixel uncooled IR (infrared) image sensor. For IR detection, we utilized single crystal silicon series p–n junctions, which were fabricated on a SOI (silicon on insulator) wafer utilizing 8 inch CMOS technology and MEMS processes. The p–n junctions were passivated with buried and laminated oxide layers from wet crystalline etching of the silicon substrate. The oxide layers were also utilized to absorb the IR radiation and to form supporting beams. The partially released pixels were utilized as thermal black pixels (TBs) instead of optical black pixels (OBs) for correlated double sampling. The IR image sensor utilizing TBs obtained a thermal image of the human body stably without the smearing phenomenon.

A nozzle-type ultra-micro-volume multi-ion sensor using a rear-gate SIS/ISFET

Abstract A nozzle-type micro multi-ion (NMM) sensor suitable for ultra-micro-volume sample-solution analysis has been developed using a newly designed rear-gate silicon-insulator-silicon (SIS) three-layer structure ISFET chip. The sensor inner volume is only 2.5 μl from the nozzle tip to the ISFET part for sensing the temperature and three types of ions. The outer body of the sensor is also sufficiently small to be dipped into the standard miniature sample vessels used in automatic blood analysers. K + , Na + and Cl - ion-sensing membranes are formed on the ISFET, and their basic characteristics and durabilities are checked. Furthermore, the sample solution volume needed for the sensor is estimated from pH and K + ion flow-through sensing measurements. As a result, the sensor durability to cleaning by a detergent solution has been more than doubled by means of the membrane-locking structure of the ISFET chip. Also, the sample volume needed for the measurement has been drastically reduced to about 20 μl including prior sample-solution rinsing.

Temperature stability improvement of a QVGA uncooled infrared radiation FPA

We have developed a low-cost uncooled infrared radiation focal plane array (FPA) requiring no thermoelectric cooler (TEC), which has 320 x 240 detection pixels with 22 um pitch. The silicon single-crystal series p-n junction diodes and the low-noise readout circuit on the same SOI wafer fabricated by 0.13 um CMOS technology were utilized for infrared (IR) detection. The temperature dependence in the readout circuit was eliminated by correlated double sampling (CDS) operation with reference pixel that was insensitive to infrared radiation. In order to reduce the temperature dependence, we improved the reference pixel and the readout circuit. Although the reference pixels should be completely insensitive to IR radiation, prior reference pixels showed measurable sensitivity. The improved reference pixel was formed by partially releasing with bulk-micromachining and was verified to be insensitive to IR radiation by an object of 400°C. The readout circuit had a differential amplifier instead of a singletransistor amplifier and an analog-to-digital converter (ADC). In each portion, CDS was applied to reduce temperature dependence. The first CDS operation was used for eliminating the pixel output variation and the second operation was used for canceling the variation of the differential amplifier. The output variation referred to input was reduced to 1/30 compared with that of the prior circuit. Moreover, the residual variation of output voltage was reduced by CDS operation in ADC and stable output data was obtained with ambient temperature variation. With these improvements, the sensitivity variation of the FPA was improved to 10% in the range of -30 degrees to 80 degrees and noise equivalent temperature difference (NETD) of 40 mK was achieved.

Scale down of p-n junction diodes of an uncooled IR-FPA for improvement of the sensitivity and thermal time response by 0.13-µm CMOS technology

We have developed an uncooled infrared radiation focal plane array (IR-FPA) with 22 μm pitch and 320 × 240 pixels utilizing silicon p-n junction diodes, which were fabricated by 0.13 μm CMOS technology and bulk-micromachining. The thermal time response of cells was lowered to be 16msec by reduction of thermal capacity of cells. In addition to increase the sensitivity of cells by extending the length of supporting beams, p-n junction diode was scaled down as small as 20% in area compared to previous one. Micro-holes were formed in the cell to reduce only thermal capacity, which were negligibly small compared to incident IR wavelength. This method needs no additional process step and is considered as suitable for low cost and mass-productive IR-FPA.

A 320 x 240pixel uncooled TEC-less infrared radiation focal plane array with the reset noise canceling algorithm

We have developed a 22um pitch and 320 × 240 pixel uncooled infrared radiation focal plane array on the silicon-oninsulator (SOI) substrate by means of 0.35um CMOS technology and bulk-micromachining. For IR detection, we use silicon single-crystal series p-n junctions that can realize high uniformity of sensitivity and low voltage drift. The supporting beam shrinkage enabled the pixel pitch shrinkage from 32um to 22um and 320 × 240 pixel number without deteriorating NETD. We also developed a SOI low-noise CMOS readout circuit that can calibrate chip temperature and introduced a noise canceling digital algorithm to cancel the reset noise generated in the readout circuit. The dominant noise source, SOI MOSFET noise, was decreased by optimizing the gate design. Finally the FPA has realized noise equivalent temperature difference (NETD) of 0.12K and requires no thermo-electric cooler (TEC) and is mounted on a low-cost standard ceramic package.

Development of an ISFET-based Nutrient Sensor for Plant Growth Media.

A new type of the nutrient sensor using ISFET (ion-sensitive field-effect transistor) has been investigated. Measuring the ion concentration of a solution in plant growh media (ex. rockwool) is difficult and has not been carried out in practice. The authors anticipated that an ISFET, with its advantages of small size and low output resistance, could be used to measure the ion concentration of such a solution in growth media. In this study, the authors examined the basic characteristics of ISFET-based nutrient sensor probes in rockwool as follows : 1) response characteristics for nitrate ion concentration changes in rockwool, 2) reproducibility of the output when they were inserted into rockwool repeatedly, 3) output dependence on the rockwool water content, 4) output dependence on the distance between the ISFET and a reference electrode, 5) long-term stability of the sensitivity and output baseline in rockwool. These experiments have shown that the sensors have sufficient stability for use in this kind of measurement. The authors have found that ISFETs are able to measure the ion concentrations for a nutrient solution in growth media such as rockwool.

An Isfet-based nutrient sensor for rockwool culture

An application of ISFETs (ion-sensitive field-effect transistors) to nutrient solution control systems in rockwool culture has been investigated. Measuring the ion concentration of a solution in rockwool is difficult and has not been carried out in practice. The authors anticipated that an ISFET, with its advantages of small size and low output resistance, could be used to measure the ion concentration of such a solution in rockwool. In this study, the authors examined the basic characteristics of ISFET-based nutrient sensor probes in rockwool. The characteristics examined were as follows: 1) Sensitivity characteristics for certain ion concentration changes (over a 10−4-10−1M NO3− range). 2) Reproducibility of the output when they were inserted into rockwool repeatedly. 3) Output dependence on the rockwool water content (over a 2080% range). 4) Output dependence on the distance between the ISFET and a reference electrode (over a 10-80 cm range). 5) Long-term stability of the sensitivity and output baseline in rockwool (over 2 weeks). These experiments have shown that the sensors have sufficient stability for use in this kind of measurement. The authors have found that ISFETs are able to measure the ion concentrations for a nutrient solution in rockwool culture.