Abstract: A micro-hotplate is provided in the form of a device comprising a sensor and one or more resistive heaters within the micro-hotplate arranged to heat the sensor. Furthermore a controller is provided for applying a bidirectional drive current to at least one of the heaters to reduce electromigration. The controller also serves to drive the heater at a substantially constant temperature.

Abstract: A micro-hotplate is provided in the form of a device comprising a sensor and one or more resistive heaters within the micro-hotplate arranged to heat the sensor. Furthermore a controller is provided for applying a bidirectional drive current to at least one of the heaters to reduce electromigration. The controller also serves to drive the heater at a substantially constant temperature. Such an arrangement is advantageous over an arrangement in which a unidirectional DC drive current is applied to the heater. This is because the unidirectional drive current causes electromigration which results in an increase in resistance over time. This is undesirable because it can lead to failure of the micro-hotplate. In contrast, the application of the bidirectional current reduces electromigration and as a result there is insignificant change in the resistance of the heater over time and under high temperature.

Abstract: A gas-sensing semiconductor device 1? is fabricated on a silicon substrate 2? having a thin silicon dioxide insulating layer 3? in which a resistive heater 6 made of doped single crystal silicon formed simultaneously with source and drain regions of CMOS circuitry is embedded. The device 1? includes a sensing area provided with a gas-sensitive layer 9? separated from the heater 6? by an insulating layer 4?. As one of the final fabrication steps, the substrate 2? is back-etched so as to form a thin membrane in the sensing area. The heater 6? has a generally circular-shaped structure surrounding a heat spreading plate 16?, and consists of two sets 20?, 21? of meandering resistors having arcuate portions nested within one another and interconnected in labyrinthine form.

Abstract: A gas-sensing semiconductor device 1? is fabricated on a silicon substrate 2? having a thin silicon dioxide insulating layer 3? in which a resistive heater 6 made of doped single crystal silicon formed simultaneously with source and drain regions of CMOS circuitry is embedded. The device 1? includes a sensing area provided with a gas-sensitive layer 9? separated from the heater 6? by an insulating layer 4?. As one of the final fabrication steps, the substrate 2? is back-etched so as to form a thin membrane in the sensing area. The heater 6? has a generally circular-shaped structure surrounding a heat spreading plate 16?, and consists of two sets 20?, 21? of meandering resistors having arcuate portions nested within one another and interconnected in labyrinthine form.

Abstract: 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.