Microthruster with integrated platinum thin film resistance temperature detector (RTD), heater, and thermal insulation

Abstract

We have fabricated microthruster chip pairs - one chip with microthruster structures such as injection capillaries, combustion chamber and nozzle, the other chip with platinum thin film devices such as resistance temperature detectors (RTDs) and a heater. The platinum thin film was sputtered on thermally oxidized silicon wafers WITHOUT adhesion layer. The effects of anneal up to 1050°C on the surface morphology of platinum thin films with varied geometry as well as with / without PECVD-SiO₂ coating were investigated in air and N₂ and results will also be presented. Electrical characterization of sensors was carried out in a furnace tube in which the sensors' temperature was varied between room temperature and 1000°C with a ramp of ±5Kmin^-1 in air and N₂. The experiments showed that the temperature-resistance characteristics of sensors had stabilized after the first heating up to 1000°C in N₂. After stabilization the sensors underwent further 8 temperature cycles which correspond to over 28h of operation time between 800 - 1000°C. To reduce the loss of combustion heat, chip material around the microthruster structures was partially removed. The effects of thermal insulation were investigated with microthruster chip pairs which were clamped together mechanically. The heater power was varied up to 20W and the temperature distribution in the chip pairs with / without thermal insulation was monitored with 7 integrated thin film sensors.