Simple detector pixel of dielectric bolometer mode and its device structure for an uncooled IR image sensor

Abstract

A new type of simple pixel circuit has been developed in an IR image sensor of dielectric mode (DB). The detector pixel consists of capacitors of ferroelectric BST thin film prepared by laser ablation, whose dielectric constant changes drastically with temperature. Our new circuit is a serially-connected capacitor-capacitor circuit with a source-follower output buffer, where one capacitor is an IR detecting BST thin film capacitor formed on a membrane and the other is the same capacitor as reference but on Si bulk and nonirradiated. In order to avoid crack and deformation on the thermally insulated structure, a stress-balanced structure by multi-layered membrane has been newly developed, where the ferroelectric capacitor is formed on a triple layer of SiO2/SiNx/SiO2 films. A BST film on membrane is found to show positive TCD ranging from 1 to 6 percent K in our experiment. A new monolithic process flow is developed to combine an n-MOSFET process and a Si-bulk micromachining process, and ferroelectric capacitors on the stress-balanced membrane are able to be formed monolithically with MOSFET's for source-follower output buffer. Finally, it is especially noted that the operation in the detector pixel in the DB mode is confirmed on the monolithically integrated device structure.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.