Design, fabrication, and characterization of bridge-type micro-hotplates with an SU-8 supporting layer for a smart gas sensing system

Abstract

In this study, bridge-type micro-hotplates (MHP) with an SU-8 supporting layer were proposed for smart gas sensor applications. The proposed MHP consisted of a heating membrane with an area of 140 µm × 140 µm, and a 33 µm-thick SU-8 layer deposited on its bridges. Finite element method based simulation confirmed that the proposed MHP displayed good thermal isolation properties. The proposed MHP was successfully fabricated, and the properties of the MHP were characterized. Current–voltage characteristics revealed that the MHP temperature can reach 550 °C at 5 V. The temperature of the MHP was calculated from changes in the resistance of the heater. Power consumption of the MHP approximately corresponded to 13.9 mW for heating to 300 °C. This was comparable to the power consumption reported in the previous studies. Furthermore, a stable operation under a constant voltage was observed for 100 min. The properties of the MHP indicated that it could potentially be utilized for applications related to integrated gas sensors.

CO2 Sensing Characteristics of a La2O3/SnO2 Stacked Structure with Micromachined Hotplates

“…Figure 5a shows the current–voltage ($I-V$) characteristics of the heater. In addition, the heater temperature calculated from the heater resistance [28] was plotted on the graph. It was confirmed that the MHP can be heated to approximately 530 °C at 5 V. The heater temperature plotted against the power consumption of the heater is shown in Figure 5b.…”

“…The membrane area was 140 $\mathsf{\mu }$m × 140 $\mathsf{\mu }$m, and the effective area of the device including the bridges was approximately 270 $\mathsf{\mu }$m × 270 $\mathsf{\mu }$m. The fabrication details of the MHP are described elsewhere [28]. …”

Microhotplates for Metal Oxide Semiconductor Gas Sensor Applications—Towards the CMOS-MEMS Monolithic Approach

“…Efforts are made to improve the mechanical stability of the suspended structure. Iwata et al [ 49 ] has proposed to reinforce the bridges with the thick polymer layer SU-8 due to its extremely low thermal conductivity ( ) compared to silicon, as well as its compatibility with micromachining processes. However, the reinforced layer increases the fabrication complexity, which is why it has not been adopted in other studies so far.…”

“…A Finite Element Method (FEM) electro-thermal simulation is commonly implemented during the microhotplate design process for optimization of the temperature distribution and power consumption. A large variety of commercially available software such as ANSYS [ 49 , 52 , 53 , 54 , 55 , 56 ], COMSOL Multiphysics [ 57 , 58 , 59 , 60 , 61 , 62 , 63 ], ConventorWare [ 64 , 65 ], ISE TCAD [ 66 , 67 , 68 ] and MEMCAD [ 69 ] has been used. Figure 6 shows the temperature distribution of a suspended membrane microhotplate without a gas sensitive layer for a target temperature of 700 °C [ 54 ].…”

“…Temperature uniformity can be improved by attaching a layer of material with high thermal conductivity to the microhotplate. The high thermal conductivity material can either be a silicon island [ 69 ] left after back side etching or a metal heat spreader plate [ 49 , 88 ] deposited above the heating element ( Figure 7 ).…”