• Journal of Sensor Science and Technology
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• v.7 no.3
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• pp.147-153
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• 1998

The strain characteristics of a fiber optic Fabry-Perot pressure sensor with high sensitivity using a $Si_{3}N_{4}/SiO_{2}/Si_{3}N_{4}$ (N/O/N) diaphragm is experimentally investigated. A 600 nm thick N/O/N diaphragm was fabricated by silicon anisotropic etching technology in 44 wt% KOH solution. An interferometric fiber optic pressure sensor has been manufactured by using a fiber optic Fabry-Perot intereferometer and a N/O/N diaphragm. The 2 cm length fiber optic Fabry-Perot interferometers in the continuous length of single mode fiber were produced with two pieces of single mode fiber coated with $TiO_{2}$ dielectric film utilizing the fusion splicing technique. The one end of the fiber optic Fabry-Perot interferometer was bonded to a N/O/N diaphragm. and the other end was connected to an optical setup through a 3 dB coupler. For the N/O/N diaphragm sized $2{\times}2\;mm^{2}$ and $8{\times}8\;mm^{2}$, the pressure sensitivity was measured 0.11 rad/kPa and 1.57 rad/kPa, respectively, and both of the nonlinearities were less than 0.2% FS.

• Journal of the Korean Vacuum Society
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• v.6 no.3
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• pp.220-226
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• 1997

An optical intensity-type pressure sensor has been fabricated by coupling multimode optical fiber with 100 nm-Au/30 nm-NiCr/150 nm-$Si_3N_4/300 nm-SiO_2/150 nm-Si_3N_4$ optical reflection layer supported by micromachined frame-shape silicon substrate, and its characteristics was investigated. For the application of $Si_3N_4/SiO_2/Si_3N_4$ diaphragm to the optical reflection layer of the sensor, NiCr and Au films were deposited on the backside of the diaphragm by thermal evaporation , respectively, and thus optical low caused by transmission in the reflection layer could be decreased to a few percents. Dielectric diaphragms with uniform thickness were able to be also reproduced because top- and bottom-$Si_3N_4$ layer of the diaphragm could automatically stop silicon anisotropic etching. The respective pressure ranges in which the sensor showed linear optical output power-pressure characteristics were 0~126.64 kPa, 0~79. 98 kPa, and 0~46.66 kPa, and the respective pressure sensitivities of the sensor were about 20.69 nW/kPa, 26.70 nW/kPa, and 39.33 nW/kPa, for the diaphragm sizes of 3$\times$3 $\textrm{mm}^2$, 4$\times$4 $\textrm{mm}^2$, and 5$\times$5 $\textrm{mm}^2$, indicating that the sensitivity increases as diaphragm size increases.