A novel cold-wall MOCVD method for fabrication of a durable micro-machined SnO2 gas sensor

A novel cold-wall metal organic chemical vapor deposition (MOCVD) method has been developed to fabricate a durable micro-machined SnO2 thin-film gas sensor. Instead of using a hot plate or a heater around a reactor, a microheater fabricated using micromachining technology is put into the reactor and used as the heat source for thermal decomposition of the metal organic source. Since SnO2 film is selectively deposited on the microheater using this method, no patterning process for the SnO2 film is necessary. Moreover, the durability of the sensor fabricated using this method (N-sensor) is considerably improved compared with that of a sensor fabricated by a conventional hot-wall MOCVD method (C-sensor). The N-sensor outlasted over seven million heat cycles (500 degrees C for 100 ms and room temperature for 100 ms), while the C-sensors were broken after a few hundred thousand heat cycles. Although the N-sensor demonstrated excellent durability, its sensitivity for methane gas was low. However, the sensitivity of the method may be improved by optimizing the deposition conditions.