Comparisons between Membrane, Bridge and Cantilever Miniaturized Resistive Vacuum Gauges

Abstract

Using bulk micromachining, meander-shaped resistor elements consisting of 20 nm Cr and 200 nm Au were fabricated on 1 μm thick silicon nitride membranes, bridges, and cantilevers. The resistance change as a function of pressure depends strongly on the thermal resistance of the two metal lines connecting the heated resistor to the silicon bulk (cold junction) and on the thermal resistance of the silicon nitride. Relative resistance changes ranging from about 3% (small membrane) to 20% (bridge) per mW of input power were obtained when operating the devices in constant voltage mode. The pressure where maximum sensitivity of these gauges occurs depends on the distance ‘d’ between the periphery of the heated resistor element and the silicon cold junction. Devices with ‘d’ ranging from 50 μm to 1,200 μm were fabricated. Assuming that pressures can be reliably measured above the 10% and below the 90% points of the resistance versus pressure curve, the range of these devices is about two orders of magnitude. By integrating two devices, one with d = 65 μm and one with d = 1,200 μm on the same chip and connecting them in series, the range can be increased by about a factor of three. By fabricating the cantilever devices so that they curl upon release, it will be shown that these devices also exhibit larger range due to varying ‘d’.

Integration of a MEMS-type vacuum pump with a MEMS-type Pirani pressure gauge

“…la). The gauge, consisting of a meander heater made of Crl Au bilayer, deposited onto a thin silicon nitride bridge (l000x200x 1.0 /!m) [2] has been encapsulated in a miniature glass container ( fig. 1 b).…”

Optimized MEMS Pirani sensor with increased pressure measurement sensitivity in the fine and rough vacuum regimes

“…By miniaturizing the sensor element, new application fields are gathered. The new sensor elements are much smaller in size and are competitive 2,4,5, [11][12][13]21,[28][29][30][31][32][33][36][37][38]42,45 with or even improved 1,3, 15,17,[23][24][25]43 in sensitivity compared to conventional Pirani gauges. Many designs [6][7][8][9][10][14][15][16][17][18][19][20]22,26,34 have been developed for specific pressure ranges.…”

The Micro Pirani Gauge with Low Noise CDS-CTIA for In-Situ Vacuum Monitoring

“…Most effective method of increasing the high pressure limit of the dynamic range is to reduce the gap between the Pirani gauge and the heat sink [6]. And the area of Pirani gauge also has an effect on the pressure range [7]. The heat loss, Q loss is mainly contributed to thermal convection through the residual gas, conduction through contacts and leads and thermal radiation between sensitive material and substrate.…”