Enhanced Infrared Absorbance of the CMOS Compatible Thermopile by the Subwavelength Rectangular-Hole Arrays

Abstract

The enhanced infrared absorbance (IRA) of the complementary metal-oxide-semiconductor (CMOS) compatible thermopile with the subwavelength rectangular-hole arrays in active area is investigated. The finite-difference time-domain (FDTD) method considered and analyzed the matrix arrangement (MA) and staggered arrangement (SA) of subwavelength rectangular-hole arrays (SRHA). For the better cases of MA-SRHA and SA-SRHA, the geometric parameters are the same and the infrared absorption efficiency (IAE) of the SA type is better than that of the MA type by about 19.4% at target temperature of 60 °C. Three proposed thermopiles with SA-SRHA are manufactured based on the 0.35 μm 2P4M CMOS-MEMS process. The measurement results are similar to the simulation results. The IAE of the best simulation case of SA-SRHA is up to 3.3 times higher than that without structure at the target temperature of 60 °C. Obviously, the staggered rectangular-hole arrays with more appropriate geometric conditions obtained from FDTD simulation can excellently enhance the IRA of the CMOS compatible thermopile.

A Thermopile Device with Sub-Wavelength Hole Arrays by CMOS-MEMS Technology

“…The thin film of the thermopile has a smaller heat capacity and solid thermal conductance. The thorough heat exchange mechanism is shown in Figure 2 [ 24 , 52 ]. In general, the dynamic thermal behavior of the infrared sensing element is described by the heat equation which includes the heat radiation exchange mechanism between the infrared radiation source and the sensor and also solid conduction, convection which are all described in Equation (1).…”

“…Based on the 0.35 μm 2P4M CMOS-MEMS process in TSMC [ 16 ], the thermopiles with specific SHA are designed and fabricated [ 24 , 52 ]. To accurately construct the SHA design model, it is necessary to understand the 0.35 μm 2P4M CMOS-MEMS process.…”

“…To search the SHA geometric parameters with better results, an accurate and efficient simulation tool is necessary. Based on the FDTD method, the simplified simulation model is setup by following the design rules of the TSMC 2P4M CMOS-MEMS process and considering the computational efficiency [ 24 , 52 ]. The so-called simplified simulation model that the simulation model only considers the IR light wave propagation on the active area and the materials of active area are simplified to consider only one layer of SiO 2 .…”

“…From Figure 9 , it is found that the result of ρ R = 2.5 μm is better than ρ R = 3.0 μm. Moreover, according to trial production experience seen from Table 3 , the actual limit of the process line width is 2.5 μm [ 52 ]. So that, for the further optimization of trial production, the minimum structure line width is taken as 2.5 μm, that is, ρ R = ρ S = ρ C = 2.5 μm.…”

“…Based on CMOS-MEMS technology, an integrated and miniaturized thermopile sensor with various SHAs is proposed [ 24 ], and the influence of geometry on the infrared absorption efficiency (IAE) of some different types of SHAs is further studied [ 24 , 52 ]. The square and hexagonal patterns are considered to arrange subwavelength rectangular hole array (SRHA) [ 52 ]. The FDTD simulation results shows the cases of square arrangement (SA) are better than those of hexagonal arrangement (HA) in similar conditions.…”