Vol.5 No.3 2012

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Research paper : Development of a pressure sensor using a piezoelectric material thin film (M. Akiyama et al.)−173−Synthesiology - English edition Vol.5 No.3 (2012) property of piezoelectric thin films• Development of the technology to evaluate the property of piezoelectric thin films in high temperature environment• Design of sensor element and sensor housing• Development of the fabrication technology• Development of the technology to evaluate the performance of the sensor by engineThe second stage is currently in progress, and the selection of the component materials for the combustion pressure sensor for mass-produced cars by the integration of these elemental technologies, prototype sensor fabrication, and performance evaluation tests are being done. In the above scenario, we hope to contribute to the development of control technology for the next-generation high-performance engine.At the beginning of the R&D, it was assumed that the development of a combustion pressure sensor for mass-produced cars would progress by replacing the piezoelectric parts, which is the detecting material of the commercial combustion pressure sensor, if the piezoelectric property of the AlN thin film could be clarified. However, when the actual joint research was done, the automotive parts company did not have much experience in studying the piezoelectric combustion pressure sensor. Therefore as the research progressed from the development of the technology to fabricate the piezoelectric thin films to the development of the technology to evaluate the electric property of piezoelectric thin films, the development of the technologies to evaluate the property of piezoelectric thin films in high temperature, to design and fabricate the sensor element and housing, and to evaluate the sensor performance with an engine were conducted concurrently, with the cooperation of the automotive parts company and the university.In the performance evaluation test, the commercial piezoelectric combustion pressure sensor was set as the evaluation standard. Since the output (sensitivity) of the piezoelectric combustion pressure sensor is largely affected by the form of the sensor, the evaluation was done based on how close the product approached the response waveform of the commercial sensor, rather than directly comparing the sensor output values.Since the sensor output in a certain set range is necessary for installment in mass-produced cars, the R&D was done considering the structure that allowed adjustment of the sensor output after the performance evaluation. At the same time, the practical issues of the prototype sensor that were not considered during the initial performance tests were investigated, and revisions and improvements were conducted to create the combustion pressure sensor that was as close to the completed product as possible. The above R&D was conducted jointly by AIST, the automotive parts company, and Meiji University. The individual specialties and experiences were gathered for the technologies for thin film fabrication, analysis of the property and phenomenon in high temperature environment, dynamic analysis, sensor design, and others. The team from the Measurement Solution Research Center, AIST was in charge of the development of technologies to fabricate the piezoelectric thin films, to evaluate the electric property of piezoelectric thin films, to evaluate the property of piezoelectric thin films in high temperature, to design and fabricate the sensor element and housing, and to evaluate the sensor performance with an engine. The Meiji University team worked on the development of technologies to design and fabricate the sensor element and housing, and to evaluate the sensor performance with an engine. The automotive parts company team worked on the development of technologies to design and fabricate the sensor element and housing from the standpoint of auto-parts manufacturing, and conducted the performance and durability tests of the sensors in severe environments. The team from the Energy Technology Research Institute, AIST was also in charge of the performance and durability tests of the sensors in severe environments.In this R&D, a place for sharing the information and exchanging opinions were set for the teams and members. Mutual attendances to the performance tests and application tests were arranged, to take advantage of the joint project as much as possible.The following section of the paper is the outline of the development of the core elemental technology and the performance evaluation of the prototypes, in the R&D of the combustion pressure sensor. 3 Fabrication and evaluation of the piezoelectric thin films3.1 Selection of the piezoelectric material and thin film fabricationThe authors’ team selected aluminum nitride (AlN) as the detection material for the following reasons: 1) shows highest service temperature limit at 1200 °C among the piezoelectric materials, 2) does not contain hazardous elements such Table 1. Comparison of major characteristics of piezoelectric materialEase of fabricating the thin filmService temperature limit (℃)Piezoelectric constant d33 (pC/N)GoodPossibleImpossibleImpossibleImpossibleExcellent100012009202503501200635625026La3Ga3SiO14LiNbO3GaPO4Pb(Zr,Ti)O3SiO2AIN

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