Advancements of uncooled infrared microbolometer materials: A review

In this review, we have comprehensively elaborated on the various materials suitable for the infrared (IR) bolometer applications and also provided the underlying mechanisms of various reported device structures. IR bolometers are used for thermal imaging, operates by changing the resistance of the sensing layer upon absorbing the IR radiation from the source and which in turn modifies into the electric output signals. We first look at the most fundamental developments associated with the materials and device architecture for advancements in the uncooled microbolometers. Starting from traditional materials like α-Si and VO x , and novel materials like carbon nanotubes (CNTs) and few metal oxides, we have given special attention to enhancement in the temperature coefficient of resistance (TCR) of the bolometric materials for improving the device performance. Specifically, most of the uncooled microbolometer technology is dominated by the conventional materials, like VO x and amorphous (α)-Si in terms of performance and large-scale production. The α-Si based microbolometers are able to achieve the TCR values about − 3%/K at room temperature. However, the boron (B) doping and hydrogenated-Si (Si:H(B)) enhances the TCR value (−4.5%/K). The framework of VO x film with gold-black IR absorber provide the TCR about − 2.4%/K along with high responsivity (8.4 ×10 4 V/W). Recent advancements in the development of metal oxide (TiO 2−x ) based thin films enable very high TCR values (−2.56%/K) along with lower 1/f noise parameter (3.16 ×10 -12 ). These findings can be understood in terms of much sensitive oxygen vacancies to control the device performance. In addition, TCR values can be further tuned along with the reduction of noise through the interfacial interaction with CNTs and other doping elements. Therefore, non-stoichiometric TiO 2−x thin films serves as potential candidate to replace the traditional α-Si and VO x based uncooled microbolometers. • Systematically classified the microbolometer materials based upon their performance. • Basic mechanism and prominent figures of merit of microbolometers are explained. • The dependence of TCR performance on various bolometric materials are discussed. • Most recent advancements in uncooled bolometers are addressed by expound of their problems.