Electro-optical Phase Shifter Array Using Ferroelectric Thin Films

Electronic scanning technology which is achieved by optical phased array has important application in military radar. The basic cell of optical phased array is light phased-shifter. Ferroelectric thin films Lanthanum-modified lead zirconate titanate (PLZT) and barium strontium titanate (BST) have many excellent properties such as strong electro-optic effects, fast response speed, high thermal stability and strong laser endurance, so they can be used to fabricate light phased-shifter. One of the transparent conductive thin films indium tin oxides (ITO) was selected as electrode of PLZT and BST. ITO thin films based on quartz were prepared by sputtering, and chemical wet-etching was used to micro-pattern of ITO. Electro-optic effects of PLZT and BST were studied in this paper.This paper studied wet-etching method of ITO thin films, it etched by mixed solution of (p(HCl:HNO₃:H₂O) = 50:3:50 with etching rate of 30nm/min at 35℃. ITO thin films etched selectivity relative to ferroelectric PLZT and BST thin films which prepared by sputtering and thermal treatment is more than 17:1.This paper studied preparation process parameters of PLZT (8/65/35) thin films with high optical and electro-optic properties. PLZT thin films which deposited on ITO/quartz were annealed at 700℃for 20min in lead atmosphere. In the range of visible light, the average transmittance is 81.3%, corresponding sideband wavelength at 350nm; the refractive index is 2.2 at the wavelength of 632.8nm; the extinction coefficient k is small than 0.040; the absorption coefficient a is 0.031×10⁵cm(-1), corresponding energy gap is 3.41eV. PLZT thin films have high-orders electro-optic effects, linear electro-optic coefficient r is 3.5×10^-6m/V, quadratic electro-optic coefficient R is 2.9×10^-16m²/V², third-order electro-optic coefficient is 8.9×10^-24m³/V³ and forth-order electro-optic coefficient is 1.4×10^-31m⁴/V⁴.BST(60/40) thin film on ITO/quartz was annealed at 700℃for 20min. In the range of visible light, the average transmittance is 83.0%, corresponding sideband wavelength at 350nm; the refractive index is 2.44 at the wavelength of 632.8nm; the extinction coefficient k is small than 0.013; the absorption coefficient a is 0.038×10⁵cm^-1, corresponding energy gap is 3.68eV. BST thin films have high-orders electro-optic effects, linear electro-optic coefficient r is 2.5×10^-9m/V, quadratic electro-optic coefficient R is 2.3×10^-16m²/V², third-order electro-optic coefficient is 9.4×10^-24m³/V³ and forth-order electro-optic coefficient is 1.3×10^-31m⁴/V⁴.These results indicate that both PLZT and BST thin films prepared on ITO/quartz substrate by RF sputtering have excellent optical and electro-optic properties. PLZT thin films have stronger electro-optic memory effects than BST thin films. They can be used to fabricate high performance electro-optic devices.