Micromachined integrated pressure—thermal sensors on flexible substrates

Abstract

This paper presents the design, modeling and simulation of micromachined, integrated pressure-thermal sensors on flexible polyimide substrates. Finite element simulations were performed with polycrystalline silicon as the piezoresistor material on a suspended Si 3 N 4 layer. These piezoresistors are connected to each other in a half-bridge Wheatstone configuration using flexible aluminum interconnects. Several different designs of integrated thermal-pressure sensors as well as pressure-only sensors were simulated to compute the sensor figures of merit such as the percentage change in piezoresistance in response to normal pressure, piezoresistor Wheatstone-bridge output voltage for varying skin curvature, bolometric response to broadband infrared radiation, thermal time constant and thermal conductance of the micromachined structures hosting the sensors to the substrate. For a perpendicular uniform pressure application of 50 kPa, a maximum Wheatstone-bridge output of 7.59 mV was computed for 1 V bias, corresponding to a piezoresistance change of 1.52%. When the skin is bent to a curvature of 2.2 mm, a maximum Wheatstone-bridge output voltage of 70 mV was calculated for the case when the sensors are aligned along the axis of bending. Thermal and optical calculations performed on the integrated thermal-pressure sensors showed a thermal time constant as low as 12.8 µs for a 1.9 µm thick silicon nitride membrane layer, with a responsivity of 270 V W −1 to a broad-band infrared radiation. This would be appropriate for applications requiring fast response but not high sensitivity. Integrated sensors on a thinner silicon nitride membrane layer of 0.5 µm, on the other hand, exhibited responsivity as high as 2000 V W −1 , with a response time of 626 µs.

Nanoscale Patterning and Electronics on Flexible Substrate by Direct Nanoimprinting of Metallic Nanoparticles

“…as the substrates for electronic and display devices. These applications include flexible organic light-emitting displays, [1,2] thin film transistors, [3][4][5] sensors, [6,7] and polymer MEMS. [8,9] The advantages of polymer-based materials are their mechanical flexibility, light weight, enhanced durability, and low cost compared with rigid materials (such as silicon and quartz).…”

Characterization of MEMS piezoresistive pressure sensors using AFM

“…In this case, the probe-tip contact force would be distributed in an area much smaller than the suspended Si 3 N 4 diaphragm area of 80 Â 80 mm 2 , as per the design specifications described in [7]. Therefore, to effectively increase the contact area of the probe-tip on the diaphragm surface, the tip was modified by attaching a spherical soda-lime glass particle of radius 25 mm to its end.…”

“…Our fabricated sensor structures [6] have diaphragm sizes ranging from 40 Â 40 mm 2 to 80 Â 80 mm 2 and a maximum deflection of 1.5 mm. They consist of a suspended 1.5 mm thick silicon nitride (Si 3 N 4 ) diaphragm with piezoresistive polysilicon resistors on the bridge arms connecting the diaphragm to the silicon substrate, in half-Wheatstone bridge configuration [7]. The schematic and 3-D solid Coventor TM model of one of the sensors are as shown in Fig.…”

Surface modification and metallization of polycarbonate using low energy ion beam

“…These devices commonly use polymer materials as substrates, which have the advantages of low density and enhanced stretchability compared to silicon (Si) substrates (Sim et al, 2013). The use of polymer substrates has resulted in new applications including flexible displays (Jin et al, 2009;Katsuhara et al, 2010), solar cells (Krebs et al, 2009) and electrical sensors (Shamanna et al, 2006), demonstrated that the stability and mechanical reliability of such devices are still a challenge. The growth of electrical resistance of thin metal films on polymer substrates was investigated by several groups for copper on Polyimide (Lu et al, 2009;Hu et al, 2011;Niu et al, 2007), Al on Polyimide (Macionczyk and Brückner, 1999;Alaca et al, 2002) and…”