Chemical Sensors

Vol. 11, No. 2 (1995)

Abstracts


シリコン化学センサの新展開を期待する

石川　孝明

新電元工業株式会社

For a New Step of Silicon Chemical Sensors

Takaaki ISHIKAWA

SHINDENGEN ELECTRIC MFG. CO., LTD.

　半導体センサと呼ばれるものはずいぶん古くから実用化されていたように思う。ところが、いわゆるシリコンテクノロジーを活かしたシリコン化学センサとなると、私が思いつくのは、せいぜい弊社が扱っているISFETだけである。それも既に２０年の歴史を持ちながら未だしの感が強い。シリコンテクノロジーを活かした化学センサの新展開が何故進まないのか。思いつくところを述べてみたい。ISFETを通じて化学センサ分野に携わるようになってまだ日が浅く、又浅学の故もあって少々的外れなところがあると思うがご容赦頂きたい。
　シリコンの半導体表面は、非常に敏感な性質を持っている。通常の半導体デバイスではこの敏感性を避けて、如何に表面を安定させるかに努力されてきた。これに対しISFETはこの敏感性を利用しているものであり、しかも半導体が最も嫌うナトリウムの様なイオンを多量に含む溶液に漬けるなど過酷な環境下で使用される。この為、有用な感応膜のアイデアが出されても安定・長寿命が要求される実用化段階で、多くの場合行き詰まってしまうのである。センサ性能と安定・長寿命の両立については、多くの方々の努力にもかかわらず、その壁は依然として残っているのが現実であろう。シリコン化学センサの新展開に当たって、改めて実用化に対する技術突破の必要性を感じている。
　更に感じることは、性能面の課題に加え一方では高機能化、知能化への展開があると思うが、そのイメージが今一つ明確になっていない様に思えることである。人間の目や耳に相当するセンシング分野では、光集積センサの例に見られるようにセンサデバイスの高性能化とともに、半導体集積技術をベースに高機能化、知能化への活動が活発に展開しつつある様に私には見える。一方、人間の鼻や耳に相当する機能の実現は化学センサの分野であろうと思うが、化学センサの高機能化、知能化への展開は牛歩のように思えるのである。これは一つには、予測されるニーズが多種多様であり実現すべき高機能化、知能化センサのコンセプトがなかなか得難いことに起因しているとも思われる。まずは原点に戻り、次世代化学センサとして何の為に、何を目指すべきか、そのコンセプトを構築していくことが大切であろうと思う。とは言っても、私自身具体イメージが描けていないし、又問題もあろうかと思うがあえて心情的に言えば、次世代シリコン化学センサの新展開をシリコン集積化技術と情報処理技術をベースにマルチ化、高機能化を目指したインテリジェントシリコン化学センサに求めたいのである。
　シリコン化学センサの関連分野は、化学、半導体、情報、光学、医学、バイオ、エコロジ等々思いつくだけでもかなりの広範囲にわたっている。それぞれの分野が創造的に新融合し、その総合力で現状の壁を打破したいものである。幸いにして本研究会には多くの企業、大学、研究機関の研究開発者やユーザーの方々が参加され、友好的に交流を深め様々な活動を展開されておられるので、シリコン化学センサの新展開に対し本研究会への期待も大きい。
　今後、本研究会がますます発展されることを願っております。



バイオセンサ

長谷部　靖

埼玉工業大学・工学部
〒369-02 埼玉県大里郡岡部町普済寺1690

Chemical Sensors 1994-Biosensors

Yasushi HASEBE

Saitama Institute of Technology
1690 Fusaiji Okabe, Saitama 369-02, Japan

緒言
　1960年代に登場した酵素膜電極は、バイオサイエンスやテクノロジーの急速な進展とともに発展し、現在では多くのバイオセンサが実用化に至っている。そして新しい測定原理も次々と提案され、センサ応答の理論的な解析等の基礎的研究や、実用的ニーズに対応する高性能かつコンパクトな応用研究に至るまで、さまざまな領域においてバイオセンサに関する研究が活発に展開されている。
　1994年は、化学センサ、バイオセンサの国際会議が、Rome(Italy)およびNew Orleans (USA)で開催され、興味ある最新の研究成果が多数報告された。
　本稿では、1994年度に発表されたバイオセンサ関連の総説、研究論文を中心に記述するが、この領域の研究は確実に増加しており、そのすべてを網羅することは筆者の能力を超えているため、不十分、不明瞭な箇所に関しては他の優れた成書や総説を参照されたい。



静電容量型ガスセンサ

石原　達己

大分大学工学部応用化学科
〒870-11 大分市大字丹野原700

Capacitive-type Gas Sensor

Tatsumi ISHIHARA

Department of Applied Chemistry, Faculty of Engineering, Oita University
Oita 870-11, Japan

Status of capacitive-type gas sensor were reviewed. Although the number of the studies on the capacitive-type sensor is limitted at present, capacitive-type sensor have a great potential as the gas sensor, since the miniaturization and combination with other type sensor are easily attained. In this article the applications of grain junction between the different semiconducting oxides to CO2 and NOx gas sensor were reviewed. Since width of the depletion layer formed at the grain junction depend on the amount of adsorbed gas, the grain junction between oxide with different semiconductivity is applicable for the detection of gases. It was found that CuO-BaTiO3 system and CoO-In2O3 system was suitable for CO2 and NO sensor, respectively. The characterization of the energy barrier formed at the grain junction was further mentioned.

緒言
　ガス漏れ警報器をはじめ、種々の分野でガスセンサが実用化されている。現在、主に使用されているガスセンサの検知方式としては、酸化物半導体型、固体電解質型、ガルバニ電池型などであり、その方式はいずれも直流測定に関連した信号処理を用いている。一方、交流測定は周囲の測定環境の影響を受けにくく、高いS/N比が得られ、増幅も容易なので、高感度な分析に適すると考えられる。現在までにインピーダンスの変化を利用したセンサが検討されているが、静電容量の変化を利用したセンサは湿度センサが検討されているのみで、ほとんど研究が行われていないのが現状であろう。しかし、静電容量型のセンサは小型化が容易であり、また信号の取り扱いや他の方式のセンサとの複合化も容易なので、化学センサとして高い可能性を有すると考えられる。そこで、本稿では静電容量型センサの開発の現状をまとめるとともに、現在、筆者らが行っている静電容量型のCO2およびNOセンサについてまとめた。



Sensor Research at University of East Anglia(UEA)

M. J. COOK, D. A. RUSSELL
School of Chemical Sciences, Univ. of East Anglia
Norwich NR47TJ, UK

There are a number of faculty in the School of Chemical Sciences, UEA whose research involves the development of novel materials and techniques for the development of chemical and biosensors.
Professor M. J. Cook (MJC) and Dr G. Cooke (GC) are involved in the organic synthesis of novel macrocyclic compounds, such as phthalocyanine molecules, which are modified to achieve high selectivity and sensitivity for a number of analytes.
Dr D. A. Russell (DAR) has an analytical research group who are looking at optical sensing techniques, including fluorescence, infrared, RAIRS and surface plasmon resonance for the development of novel chemical and bio sensors using optical waveguides (both plannar and fibre).
A number of collaborations exist within the School of Chemical. For example, MJC and DAR collaborate on a number of research projects combining the synthesis expertise with that of the optical chemical sensor development. These developments have led to exciting results for NOx sensing at the low ppm level using a self-assembled monolayer sensor.
Additionally, collaborations exist with other groups at UEA and at other centres. MJC has a collaboration whereby semiconductor sensors have been devesed using the LB technique. DAR has collaborations with colleagues in the School of Chemical Sciences (Dr JR Sodeau) and Biological Sciences (Dr DJ Richardson) who together have developed highly specific metal chelators from bacterial sources and are currently developing these chelators for optical biosensing purposes. A second project in the biosensors field is the use of metalloproteins for specific environmental gas monitors again using optical spectroscopy as the detection principle.



Thick Film Chemical Sensors

J. K. ATKINSON

Dept. of Mechanical Engineering, University of Southampton
Southampton SO9 5NH, UK

The award, in June 1992, of a DTI/SERC funded LINK contract involving a partnership of the University, Siemens Plessey, Unilever Research Laboratories, the National River Authority, the Water Research Council and the Drinking Water Inspectorate was aimed at exploiting thick film technology in the production of low cost miniature sensor arrays for the determination of water quality. This research programme, initially for two and a half tears, is presently funding two postdoctoral researchers under the supervision of John Atkinson, who is a Senior Lecturer in the Department of Mechanical Engineering and the manager of the thick film unit.
The thick film sensor arrays being developed are capable of simultaneously measuring several important parameters which, when taken together, largely determine the quality of water. These parameters include conductivity, pH, temperature and dissolved oxygen concentration. Additional sensors able to determine the waterborne levels of trace elements such as ammonia, chlorine and heavy metals are currently under research with the aim of incorporating these onto the sensor arrays.
A programme of research into thick film gas sensors has been actively maintained for the past nine tears and has explored extensively the use of thick film technology for the production of low cost gas sensor arrays. Much of this work has been externally funded by the MOD and UK industry. The use of gas sensors in arrays, combined with pattern recognition techniques, has been found to offer significant improvements in gas specificity when compared with individual sensing elements used in isolation.
The chief advantages of using thick film technology for the fabrication of sensor arrays include cost and size. Conventional sensors are both expensive and bulky whilst their thick film counterparts can be fabricated as miniature devices using a screen printed batch process which, with sufficiently large batches, can result in very low production costs.



Gas Sensor Research at HSE-Calorimetric, Electrochemical and Metal Oxide Semiconductor Sensors

P. T. WALSH

The Health and Safety Laboratory, The Health and Safety Executive
Broad Lane, Sheffield S3 7HQ, UK

Gas senosr research at HSE-Sheffield (formerly Safety in Mines Research Establishment-Sheffield) began in the late 1950s. The prime objective of this early work was to develop a reliable hand-held instrument, used in coal mines, for the measurement of methane concentrations up to its lower explosive limit. This "methanometer" should improve on existing methanometers and replace the flamelamp for methane monitoring.
The resulting sensor was the "pellistor" (derived from pellet-resistor), a catalytic calorimetric sensor which superseded the bare platinum coil sensor. The principle of operation is based on the catalytic oxidation of flammable gas with atmospheric oxygen; the heat of reaction being measured as a temperature rise. In the platinum coil sensor the coil served as both heater and catalyst whereas in the pellistor the heater coil was separated from the catalyst (based on platinum group metals,typically palladium). Separation was achieved by means of a low surface area alpha-alumina support encapsulating the heater coil upon which was deposited the catalyst mixture. This allowed greater surface area of active catalyst to be used, lowering the operating temperature from approximately 1000℃ in the bare coil sensor to 500℃ in the pellistor. This also allowed a longer operation time with a battery power supply and improved the lifetime of the sensor by reducing the risk of the heater coil fusing at elevated temperatures.
The pellistor design has been and still is used in many commercial instruments for monitoring flammable gas. Despite the disadvantages of being susceptible to catalyst poisons (e.g. silicones, sulphurous gases, halogenated hydrocarbons) and giving an ambiguous response at high methane concentrations ( >10%), the simplicity, usefulness and low cost of the sensor have resulted in its widespread use in flammable gas instrumentation, particularly in hand-held monitors.
Applications of the pellistor spread to other industries besides coal mining such as the gas, chemical and petrochemical industries, both onshore and offshore. The offshore detection of flammable gas (mainly natural gas in the UK) which included higher hydrocarbons in addition to methane, brought new problems to be solved. There was now a need to develop more poison resistant pellistors, capable of withstanding silicone vapours from fire retardant materials on the platforms and sulphurous gases from natural gas. In the late 1970s and early 1980s poison resistant pellistor-type sensor were developed at HSE, using platinum group metals dispersed on high surface area supports such as gamma-alumina. Poisoning rates greater than 300 times those of conventional pellistors were achieved. However, this was at the cost of less robustness and greater baseline drift.
In addition to the development of flammable gas sensors, HSE also developed sensors for oxygen and toxic gases. During the 1960s and 1970s, liquid electrolyte potentiometric electrochemical sensors were developed for oxygen and carbon monoxide (for potential use in coal mines) and for chlorine, nitrogen dioxide and sulphur dioxide. The sensors utilised a porous PTFE membrane to control the rate of redox reaction at the platinum electrodes. These sensors had a low response time (t90 <10 sec), however the temperature coefficient of the sensor, determined by permeation of gas through the solid membrane, was appreciable.
Also, around this time, investigations began into the use of metal oxide semiconductors for the detection of mine gases, particularly carbon monoxide and other products of combustion arising from fires. Various material, including tin oxide and zinc oxide, with various dopants (e.g. platinum metals) and fabricated using a variety of techniques were investigated. The factors influencing response were characterised (e.g. operating temperature, humidity, dopant level); prototypw sensors were developed and incorporated into sensor arrays for monitoring the mine atmosphere.
In the 1980s and 1990s, instruments were developed at HSE based on tin oxide semiconductor sensors for monitoring organic vapour concentrations in factories and chemical plants. Effort concentrated on two applications: a hand-held total organic vapour monitor and a portable gas chromatograph for the quantitative determinationof individual components of a gas mixture. By control of the fabrication process, particularly ensuring uniformity of particle size distribution between sensors, reproducible sensors were developed capable of incorporation into the above two types of instrument.
Currently the emphasis of HSE's gas monitoring work is on (a) the development of specific toxic gas instrumentation for workplace air monitoring by adaptation, where possible of existing sensors; (b) development of improved sensors for workplace air monitoring by collaboration with commercial companies and academic institutions; and (c) contributing to improved standards for the performance of gas detection instrumentation used in the workplace.



Gas Sensor Research at HSE-Sensors Based on Organic Layers

S. C. THORPE

The Health and Safety Laboratory, The Health and Safety Executive
Broad Lane, Sheffield S3 7HQ, UK.

The Health and Safety Laboratory has been interested in organic semiconductor gas sensors for a number of years. A wide range of materials which respond to toxic gases in the occupational hygiene range (1) have been investigated. Early work concentrated on vacuum sublimed films of metal and metal free phthalocyanines (2,3) capable of detecting NOX. Devices have been prepared, characterised and optimised in the laboratory and prototype instruments have been built. Some of these have been successfully used underground in U. K. coal mines on behalf of Her Majesty's Inspector of Mines.
A number of other toxic gases including sulphur dioxide, ozone, chlorine and hydrogen chloride can also be detected using these films. This offers a wide range of potential applications.
Subsequent work on these devices has shown them to be capable of detecting environmental levels of the same gases. Levels as low as a few parts per billion of NOX can be detected using vacuum sublimed lead phthalocyanine films.
One of the limitations of these sensors is that they only work well when operated at elevated temperatures (typically 170℃).
More recently the work has been broadened to look at other techniques for preparing thin films, these include Langmuir Blodgett, spin coating, self assembly, sol gel, polymer dispersed and solution grown films. This has allowed the study of a wide range of substituted phthalocyanines and porphyrins (4,5,6). Devices which operate successfully at room temperature have been prepared for occupational levels of toxic gases using these materials. This work has been carried out in collaboration with a number of UK University departments.



Chemical Sensor Research in Italy

Gualtiero GUSMANO, Enricl TRAVERSA (Departimento di Ingegneria Electronica, Universita'di Roma "Tor Vergata", Via Della Ricerca Scientifica)
00133 Roma, Italy

Arnaldo D'AMICO (Departimento di Ingegneria Elettronica, Universita'di Roma "Tor Vergata", Via della Ricerca Scientifica
00133 Roma, Italy

Chemical sensors in Italy have been studied since the late 1970s. At present, there is an ever increasing interest in chemical sensor research, which is now widespread over many Institutions, either Universities or National Research Institutes, while small and medium industries are gradually increasing their interest in this field.
Many different research activities are carried out, concerning fundamental devices, chemical interfaces, biological interfaces, new materials for sensors, new detecting principles, read-out strategies, and standardization. It must be emphasized that strong collaborations exist among the many Institutions involved in chemical sensor research, and also they frequently interact with European partners. The links with Japan are less numerous, but increasingly growing, too. Direct collaborations with Japanese laboratories, either Universities or industries, are welcome and would be of great interest.
The interest of Italian industries in the chemical sensor field, which was limited some years ago, is now stimulated by a growing interaction with the research Institutions. Small and medium industries are more and more facing the sensor problems in a large variety of applications.
The spectrum of the chamical sensors studied in Italy is wide: electrochemical, electrical (resistive and capacitive), optical, and surface acoustic wave sensors are developed. A wide range of ceramic and polymer materials, in thin and thick film form, are currently studied. The main applications are for the detection of gases (O2, CO, CO2, H2, NOx, etc.) and humidity. A large activity is also in the field of biosensors.
Research (MURST), which promotes National research programmes to improve the interaction between Industries and Research Institutions, from the National Research Council of Italy (CNR), from Industries, and from the European Community. In the last case, some special programmes have been launched by the EEEEEC, involving the participation of Institutions and Industries of more than two EC countries. A big pulse to the sensor research in Italy was given by two Targeted Projects (PE) of CNR. Under the auspices of the PF MADESS (Materials and Devices for Solid State Electronics), a subproject "Sensors" was directed by Prof. A. D'Amico, and activities on materials for sensors were carried out in the subproject "Ceramics" of the PF MSTA (Special Materials for Advanced Technologies).
The aim for the future is to create in Italy at least one National Center fully oriented towards R&D in sensors, where people working on sensors can integrate their competences. One step forward is the recent creation, on February 1995, of the "Associazione Italiana Sensori e Microsistemi" (AISEM, Italian Association of Sensors and Microsystems), which is the proof of the growing interest in the sensor field in Italy. The purpose of AISEM is the creation of a stronger cultural adhesion in the field of all kinds of sensors and their applications, including micromachining technology.
The outline of the researches performed at some of the most relevant laboratories working on chemical sensors in Italy is reported in this paper.



学会レポート　第20回化学センサ研究発表会

（'95年4月3〜4日　於　東京大学教養部）

黒岩　孝明（山武ハネウェル）
石原　達己（大分大学工学部）
水谷　文雄（生命工学工業技術研究所）
矢吹　聡一（生命工学工業技術研究所）

Conference Report. The 20th Chemical Sensor Symposium.

Takaaki KUROIWA (Yamatake-Honeywell Co.)
Tatsumi ISHIHARA (Oita Univ.)
Fumio MIZUTANI (Nat'l. Inst. Biosci. & Huma-Technol.)
Soichi YABUKI (Nat'l Inst. Biosci. & Huma-Technol.)


'95 Asian Conference on Electrochemistry

（'95年5月28〜31日　於　吹田市メイシアター）

今中　信人（大阪大学大学院工学研究科）
南海　史朗（松下電器産業）

Conference Report. '95 Asian Conference on Electrochemistry.

Nobuhito IMANAKA (Osaka Univ.)
Shiro NANKAI (Matsushita Electric Industrial Co.)


第１３回センサの基礎と応用シンポジウム

（'95年6月8〜9日　於　アルカディア市ヶ谷）

佐藤　生男

神奈川工科大学工学部

Conference Report. The 13th Sensor Symposium.

Ikuo SATOH

Kanagawa Institute of Technology

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