Microhotplates based on Pt and Pt-Rh films: The impact of composition, structure, and thermal treatment on functional properties

• Pt and Pt-Rh microhotplates are fabricated on the porous anodic alumina substrates. • Addition of 11 wt. % of Rh significantly hampers the recrystallization of Pt film. • Power consumption of microhotplates during operation at 500 °C is 115 ± 14 mW. • The resistance drift of Pt-11 % Rh microheater is less than 0.5 % per day at 500 °C. • The temperature gradient in the active zone of microhotplates is less than 10 %. Recent progress in portable semiconductor and thermocatalytic gas sensors requires the development of the microhotplates with reduced power consumption, increased shock resistance, and low resistance drift. Rh is known as alloying component, which allows one to decrease the diffusion mobility of Pt in bulk resistive heating elements. Here, a comparison study on the stability of microhotplates based on Pt and Pt-Rh thin films is performed. The porous anodic alumina is used as a substrate, which provides high adhesion of the metal film and the thermal expansion coefficient compatible with Pt and Pt-Rh alloys. Morphology and crystal structure of metal films are studied after recrystallization annealing in air at the temperatures 600–810 °C. To simulate thermal effects of the microhotplates, a model based on the finite element method is developed. The perspectives of Pt-11 % Rh alloy as a material for microhotplates operating at the temperatures above 500 °C are discussed. The achieved characteristics of the fabricated Pt-Rh microhotplates on porous anodic alumina substrates allow one to use them as a universal platform for semiconductor and thermocatalytic gas sensors manufacturing.