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.)−172−Synthesiology - English edition Vol.5 No.3 (2012) On the other hand, the piezoelectric sensor that detects the charge of electric polarization of piezoelectric body is commonly used in the laboratories of universities and companies. In the piezoelectric sensor, the engine cylinder pressure received by the diaphragm is detected by the piezoelectric body. It has advantages of being small, having high response speed, and having excellent heat resistance.[1]Crystal (SiO2) is used as the piezoelectric material of the general-use piezoelectric combustion pressure sensor. However, since the phase transition point of crystal is 573 °C, the service temperature limit is about 350°C, and cooling is necessary for measurements at 400 °C or above. Therefore, new piezoelectric material with excellent heat resistance is being sought. As shown in Figure 1, material with high piezoelectric property tends to have low service temperature limit, and it is not easy to find an optimal piezoelectric material with high piezoelectric property and heat resistance. Around 1997, a product that used gallium phosphate (GaPO4) monocrystal with theoretically estimated Curie temperature of 930 °C was realized,[1] and around 2003, the product that used langasite (La3Ga5SiO14) monocrystal that does not have Curie point (phase transition point) to 1470 °C was realized.[3] Recently, a product that uses zinc oxide (ZnO) monocrystal is being proposed. While the combustion pressure sensors that use such monocrystals may have excellent heat resistance, they are generally expensive, have poor durability against mechanical impact, and have low sensor output, and therefore, are not used in mass-produced cars.As shown above, to realize a high output, low priced combustion pressure sensor that shows heat resistance at 400 °C or over and excellent durability (at least 10 years or more), completely different technological development is necessary in all aspects, including the piezoelectric material, element structure, and sensor form.With such a background, the authors simultaneously engaged in research for heat resistance, durability, high output, and low price of the combustion pressure sensor. With the objective of developing a combustion pressure sensor for mass-produced cars, we started to engage fully in the research with support from the AIST High-tech Manufacturing Project in 2003. This research was not a revision or improvement of an already existing combustion pressure sensor, but was a R&D of the world’s first combustion pressure sensor in that it employs a structure in which the sensor elements were laminated to achieve high output, by using thin films as the detecting material rather than using the conventional monocrystal, to realize durability and low cost. 2 Scenario for developing the combustion pressure sensor for mass-produced carsFigure 2 shows the scheme of the integrated scenario for the development of a combustion pressure sensor for mass-produced cars set as the final R&D goal and the necessary elementary technologies.We set the following five points as topics to focus on in the first stage of R&D, with the issues (heat resistance, durability, high output, low cost) confronting the conventional combustion pressure sensors in mind.• Development of the technology to fabricate piezoelectric thin films• Development of the technology to evaluate the electric Fig. 1 Relationship between piezoelectric constant d33 and service temperature limitAN: AIN, BT: BaTiO3, BIT: Bi4Ti3O12,GP: GaPO4, KN:KNbO3,LF4: (K0.44Na0.52Li0.04) (Nb0.86Ta0.10Sb0.04)3,LGS:La3Ga5SiO14, LN:LiNbO3, PN: PbNb2O6,PT: PbTiO3,PZNT: 0.92Pb (Zn1/3Nd2/3)O3-0.08PbTiO3, PZT: Pb (Zr0.52Ti0.48)O3, SO: SiO2Fig. 2 Elemental technologies for development of combustion pressure sensors for mass-produced cars and scenario for integrationANSOLNPNBITPTPZTBTGPKNPZNT LGSLF4110100100002004006008001000120010000Service temperature limit (℃)Piezoelectric constant d33 (pC/N)Energy Technology Research Institute, AISTSchool of Science and Technology, Meiji UniversityStep 2Step 1Development of the technology to evaluate the property of piezoelectric thin film in high temperature environmentPerformance evaluation and durability test of sensor under severe environmentDevelopment of the technology to evaluate the sensor performance by engineDevelopment of the fabrication technology / design of sensor element and sensor housingDevelopment of the technology to fabricate piezoelectric thin filmAutomotive parts companyMeasurement Solution Research Center, AISTDevelopment of the technology to evaluate the electric property of piezoelectric thin film③Performance evaluation①Selection of component material②Fabrication of sensor prototypeDevelopment of the combustion pressure sensor for mass-produced cars

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