University of Warwick

James Anthony Covington

Florin Udrea

Julian Gardner

Takao Iwaki

Julian William Gardner

A gas-sensing semiconductor device' is fabricated on a silicon substrate&#x2032; having a thin silicon dioxide insulating layer&#x2032; in which a resistive heatermade of doped single crystal silicon formed simultaneously with source and drain regions of CMOS circuitry is embedded. The device&#x2032; includes a sensing area provided with a gas-sensitive layer&#x2032; separated from the heater&#x2032; by an insulating layer&#x2032;. As one of the final fabrication steps, the substrate&#x2032; is back-etched so as to form a thin membrane in the sensing area. The heater&#x2032; has a generally circular-shaped structure surrounding a heat spreading plate&#x2032;, and consists of two setsof meandering resistors having arcuate portions nested within one another and interconnected in labyrinthine form. The fabrication of the heater at the same time as the source and drain regions of CMOS circuitry is particularly advantageous in that the gas-sensing semiconductor device is produced without requiring any fabrication steps in addition to those already employed in the IC processing apart from a post-CMOS back etch and deposition of the gas-sensitive layer. The circular design is advantageous in that it is the best solution to minimise the size of the membrane at fixed power loss and heated area.

Gas-sensing semiconductor devices

A gas-sensing semiconductor device is fabricated on a silicon substrate having a thin silicon oxide insulating layer in which a resistive heater made of a CMOS compatible high temperature metal is embedded. The high temperature metal is tungsten. The device includes at least one sensing area provided with a gas-sensitive layer separated from the heater by an insulating layer. As one of the final fabrication steps, the substrate is back-etched so as to form a thin membrane in the sensing area. Except for the back-etch and the gas-sensitive layer formation, that are carried out post-CMOS, all other layers, including the tungsten resistive heater, are made using a CMOS process employing tungsten metallisation. The device can be monolithically integrated with the drive, control and transducing circuitry using low cost CMOS processing. The heater, the insulating layer and other layers are made within the CMOS sequence and they do not require extra masks or processing.

Growing community of inventors

Sutton Coldfield, United Kingdom

James Anthony Covington