Si monolithic microbolometers of ferroelectric BST thin film combined withreadout FET for uncooled infrared image sensor

A silicon monolithic ferroelectric thin-him bolometer coupled with a readou t FET has been developed for uncooled infrared imaging applications by mean s of Si-bulk micromachining and pulsed-laser-deposited (PLD) barium stronti um titanate Ba1-xSrxTiO3 (BST) thin films. It is a new type of dielectric b olometer (DB) mode based on the strong temperature dependence of capacitanc e upon the ferroelectric phase transition. The pixel circuit is a serial pa ir of capacitors where a sensing capacitor is fabricated on a thermally iso lated membrane and a reference capacitor on bulk area. And a new purse-bias ed-operation mode has been implemented to sense the voltage change at the i nterface node between sensitive and the reference capacitors. In order to a void crack and deformation on the thermally insulated structure, a stress-b alanced structure by multi-layered membrane has been adopted, where the fer roelectric capacitor is formed on a triple layer of NSG/SiN/SiO2-stacked fi lms. A BST (75/25) film on membrane is found to show positive temperature-c oefficient of dielectric constant (TCD) ranging from 1 to 6%/K. Upon infrared irradiation on the membrane part, a capacitance difference ar ising from a temperature rise is significantly induced within the two capac itors. Thermal signals have been confirmed with one pixel bolometer tested under an infrared light irradiation. A new monolithic process flow is devel oped to combine an n-MOSFET process and a Si-bulk micromachining process, a nd ferroelectric capacitors on the stress-balanced membrane are able to be formed monolithically with MOSFETs for source-follower output buffer. The p ixel structure also shows a simple configuration, and is very effective in reducing their pixel size and then increasing the pixel density. Finally, i t is especially noted that the operation in the detector pixel in the DB mo de is confirmed on the monolithically integrated device structure. (C) 2001 Elsevier Science B.V. All rights reserved.