Zero offset drift suppression in SiC pressure sensors at 600

Abstract

Temporal drifts in zero pressure offset voltage, V oz , observed in piezoresistive silicon carbide (SiC) pressure sensors at 600 o C were significantly suppressed to allow reliable operation. By modifying the bondpad/contact metallization, the V oz relative drift velocity at 600 o C was suppressed to within ± 0.5 mV.hr-1 , for over 1000 hours. Microstructural changes within the contact metallization were analyzed with Auger Electron Spectroscopy (AES) and Scanning Electron Microscopy (SEM). This metallization scheme may improve SiC pressure sensor reliability in short duration ground/flight tests and lower temperature (~300 o C) remote pressure monitoring (i.e., geothermal, and deep well drilling). I.

Temperature Induced Voltage Offset Drifts in Silicon Carbide Pressure Sensors

“…From the AES analysis, the PtSi zone reactions are well defined. No significant Au migration through the first PtSi layer is observed, thus further confirming the diffusion barrier property of PtSi against Au reported earlier [4,5]. The observed oxygen peak at about 1600 nm was due to a thin oxide layer that formed after the first furnace anneal.…”

“…After photolithographic pattern definition the Pt layer was etched in 10:9:1 mixture of H 2 O:HCl:HNO 3 (aqua regia) at 67 o C for 8 minutes, then 70 o C for 35 seconds to create four contacts on the piezoresistors. This was the standard scheme used previously that did not completely prevent Au diffusion to the SiC interface, which compromise the integrity of the Ti ohmic contact to SiC [5,6]. In this present work, it was necessary to increase the contact metallization stack with alternating layers of TaSi 2 and Pt, which, upon reacting to form multiple PtSi layers, would create an effective diffusion barrier against Au to the SiC interface.…”

“…3(c), which showed smaller relative changes from previous values compared to sensors 200 and 201. Based on prior reported results [4][5][6], it is believed that the improved performance of sensor 202 was due to the fact that it experienced the lowest temperature (605 °C). …”

“…However, existing long term reliability challenges, largely due to drifting zero pressure offset voltage, V oz , have prevented its permanent insertion into operational systems. Previous efforts have been made to understand the mechanisms of drifting V oz during high temperature operation with the goal of developing more stable and operationally functional pressure sensors [4][5][6]. The V oz drift is unpredictable, which does not lend itself to active correction or temperature compensation.…”

Characterization of the piezoresistance in highly doped p-type 3C-SiC at cryogenic temperatures

“…17 Additionally, piezoresistive SiC pressure sensors which can operate at high temperatures have also been demonstrated. 18,19 For instance, Okojie et al developed 4H-SiC pressure sensors which can function up to 1000 K. 20 Although numerous studies have been conducted on SiC at high temperatures, the piezoresistance of the material at negative temperatures has rarely been reported. As low temperature tolerance is imperative in several elds (e.g.…”