Un-cooled Micro-bolometer with Sandwiched Thermo-sensing Layer Based on Ge Films Deposited by Plasma

Abstract

An un-cooled micro-bolometer with thermo-sensing layer sandwiched between two electrodes has been fabricated and characterized. The micro-bolometer has a “bridge” configuration for providing sufficient thermo-isolation of the thermo-sensing layer. Surface micro-machining techniques were used for its fabrication onto a silicon wafer. The support layer is of SiN and the thermo-sensing layer is a-Ge:H,F film, both have been deposited by low frequency PE CVD technique. The active area of the thermo-sensing layer is A_B = 70×66 µm². The temperature dependence of conductivity σ(T), current-voltage characteristics I(U), spectral noise density and thermal response time have been measured in order to characterize its performance characteristics. The measured activation energy of the thermo-sensing layer is E_a = 0.34 eV providing a thermal coefficient of resistance α = 0.043 K^-1. The pixel resistance is in the range of RB = (1–30)x10⁵ Ohm. Measured current and voltage responsivities are in the range of ℜ_I = 0.3–14 AW-¹ and ℜ_U = (1–2)10⁵ VW-¹, respectively. The estimated value of the detectivity is in the range of D* = (1–40)x10⁸ cmHz^1/2W^-1 and the obtained response time is τ = 1x10^-4 sec. The performance characteristics obtained in this micro-bolometer with sandwiched thermo-sensing layer make it promising for further development of IR imaging systems.