The Study of LiTaO3 Pyroelectric Thin Film IR Detectors Prepared by the Sol-Gel Process with Various Annealing Treatments
The lithium tantalite [LiTaO3, abbreviated to LT] thin films were deposited on Pt/Ti/SiO2/Si substrates by spin coating with sol-gel technology and various rapid thermal processing in this thesis. By changing the annealed layers and heating temperature(500~800¢J), the effects of various thermal treatments on the thin films growth and the related properties are studied. Besides, the dynamic response of pyroelectric IR detector using LiTaO3 films was studied. In addition, the detector with back side etching was achieved by the anisotropic wet etching of back silicon substrate. The comparisons of detectors with and without backside etching were also investigated.
Experimental results reveal that the annealed layers will influence strongly on grain size, dielectricity, ferroelectricity and pyroelectricity of LT thin films. With the increase of the annealed layers, the grain size of LT thin film increases slightly, and highly c-axis orientated LT films can be obtained for the twelve annealed layers. From 4 to 12 annealed layers, the relative dielectric constant of LT thin film increases from 35 up to 65, the dielectric loss (tand) decreases from 0.00637 to 0.00324, the coercive field (Ec) decreases from 84.79KV/cm to 46.23KV/cm, the remnant polarization (Pr) increases from 2.54 mC/cm2 to 7.36 mC/cm2, and the pyroelctric coefficient (g) increases from 2.18´10-8 C/cm2K up to 5.71´10-8 C/cm2K.
In addition, the results also show that the LT thin film possesses the largest figures of merit Fv (3.02¡Ñ10-10 Ccm/J) and Fm (4.08¡Ñ10-8 Ccm/J) at heating temperature of 700¢J with twelve annealed layers. The voltage responsivities (Rv) measured at 70 Hz exists a largest value of 8398 V/W with twelve annealed layers. The specific detectivity (D*) measured at 200 Hz has the maximum value of 1.1¡Ñ108 cmHz1/2/W with twelve annealed layers. The results show that LT12 pyroelectric thin film detector exists both the maximums of voltage responsivity and specific detecivity. Therefore, optimizing the conditions of this study, LT12 thin film will be the most suitable for IR detector application.
Finally, the voltage responsivities (Rv) of LT thin film increases from 8398 V/W to 9537 V/W, and the specific detectivity (D*) increases from 1.1¡Ñ108 cmHz1/2/W to 2.67¡Ñ108 cmHz1/2/W after backside etching. The results show that the detectivity can be improved after backside etching.
Advisor:Chen Ying-Chung; Tsai Yu-Zun; Cheng Chien-Chung; Lee Maw-Shung; Wang Yuong-Her
School:National Sun Yat-Sen University
School Location:China - Taiwan
Source Type:Master's Thesis
Keywords:sol gel method detectors pyroelectric tantalate lithium backside etching thin film
Date of Publication:07/17/2004