This paper reports a novel tiny-sized (116 μm x 134 μm) single-crystalline silicon/aluminum infrared (IR) thermopile detector, which is micromachined only from the front side of (111) wafer for IC-foundry compatible low-cost manufacturing. The tiny-sized detector consists of six serially connected p-silicon/aluminum thermocouples that show significantly higher Seebeck coefficient and lower noise compared with the traditional poly-silicon/aluminum counterparts. With the proposed symmetric helical structure, the length of thermocouple leg length as well as the thermal resistance of the detector can be enlarged within the tiny sensing area. Specific detectivity (D*) is improved by optimizing the cross-sectional area of the two thermoelectric-material layers, which is more practically effective than traditional mathematic analysis methods. The device is fabricated in a (111) wafer [instead of normal (100) wafer] by using a novel single-side micromachining technique. The testing results show that the detector achieves an ultrahigh responsivity of 342 V/W and ultrashort response time of 0.56 ms. Featuring tiny-size, low-cost, and high-performance single-point detection, many thermopile detecting units can be integrated into an IR focal-plane array (IRFPA) for high-resolution imaging.

This paper presents a tiny 0.4 mm × 0.4 mm piezoresistive absolute pressure sensor chip with a fabrication cost as low as 0.01 US$/die. With the thin-film under bulk-silicon technique, a very thin but uniform poly-silicon pressure-sensing diaphragm is formed beneath a bulk-silicon beam-island structure to accommodate piezoresistors. The thin diaphragm exhibits a high sensitivity, and the beam-island-reinforced structure helps reduce deflection and improve linearity. The sensor is fabricated using a novel scar-free micro-hole inter-etch and sealing (MIS) process. In this newly developed process, seals are removed from the diaphragm area and placed on both the single-crystalline silicon island and single-crystalline silicon frame surrounding the poly-silicon diaphragm. Thus, the thin diaphragm is kept flat and smooth, thereby enhancing the sensing performance and fabrication yield. More importantly, the diaphragm-beam-island structure is small enough to fabricate sensor chips as small as 0.4 mm × 0.4 mm. With the high-yield process, a very low fabrication cost of 0.01 US$/die is realised owing to a high throughput of 90 000 die per 6 inch wafer. The ultra-small and low-cost pressure sensor exhibits sensitivity of 0.88 mV kPa ⁻¹ /3.3 V, hysteresis of 0.15% full scale (FS), repeatability error of 0.04% FS, and non-linearity of ± 0.10% FS. Without any additional thermal compensation method, the sensor exhibits a low temperature coefficient of zero-point offset of −0.064%/°C FS and a temperature coefficient of sensitivity (TCS) of −0.22%/°C within the temperature range from −25 °C to +85 °C, at a full measurement range (i.e. full scale) of 100 kPa. With the new scar-free MIS process, the presented pressure sensor looks promising for smartphones, drones, and other consumer-electronic applications.

This paper presents a novel single-side (111)-silicon (non-SOI) fabricated tri-axis capacitive micro-accelerometer with a dual quantization electromechanical sigma-delta modulator (EM-ΣΔM) interface circuit. The fully CMOS compatible single-sided micromachining process with toroidal shaped electrical isolation structures is described. A 2.6mm×2.6mm sized tri-axis accelerometer was designed and fabricated using only the front-side of a 4-inch (111) silicon wafer. The interface circuit was based on a front-end ASIC readout circuit and a back-end dual quantization high-order EM-ΣΔM digital circuit implemented on an FPGA. The EM-ΣΔM loop adopts a multi-feedback noise shaping architecture, for which different numbers of bits for the loop quantization were analyzed. The parameters of the EM-ΣΔM loop are optimized by a genetic algorithm (GA). Acceleration sensitivities of 170mV/g (2785LSB/g), 142mV/g (2327LSB/g) and 26mV/g (426LSB/g) were measured in EM-ΣΔM closed-loop operation for the in-plane (X/Y) and out-of-plane (Z) axis, respectively. The cross-axis sensitivity was in the order of 1 to 6% and the output noise was 0.5mg to 2mg/√Hz, with a one hour bias drift of 3 to 6mg.

Flow measurement is an essential requirement in medical, industrial, automotive and environmental applications, Thanks to the rapid development of microelectromechanical system (MEMS) micro-fabrication techniques, silicon-based microflow sensor chips used as the key component of microfluidic control systems have attracted particular attentions due to the miniaturized chip-size, high precision, low power consumption, rapid response and low-cost batch-fabrication capability. Up to present, many different types of silicon microflow sensors have been proposed and developed. This paper provides a review on recently completed works on design, fabrication and properties of the MEMS-based silicon monolithic microflow sensors. Some technical challenges and application outlooks are also discussed in the paper.

This article presents the design, fabrication, and characterization of a front-sided microfabricated high-sensitive p⁺Si/Al thermopile-based gas flow sensor with high-performance, low-cost, and high-yield volume production. Compared to most of the previously reported p⁺Si/Al thermopile-based flow sensors, the proposed sensor has a higher sensitivity and faster response time by the realization of embedding the cold junction of the p⁺Si beam into the bulk silicon and optimizing the thermal insulation of the suspended dielectric membrane from the silicon substrate. The 1-D model is established and used to optimize the design of the proposed sensor in terms of key design parameters, including the dielectric membrane thickness, the height of the isolation cavity, and so on. Accordingly, a front-sided bulk micromachining technique is employed to construct the proposed gas flow sensor. Without the need for a double-sided micromachining process, a tiny size of 0.5 mm x 0.7 mm is achieved. The tested results show that the fabricated sensor has an ultrahigh sensitivity of 540 mV/(SLM)/W and a quick response time of 1.5 ms.

In this brief, a low-cost and high-yield bulk under thin-film (BUT) MEMS technique for the volume production of flow sensors is proposed and developed. The IC-foundry-compatible process is conducted only from the front side of (111) silicon wafers, without double-sided alignment exposure, wafer bonding, cavity silicon on insulator, and double-sided polished wafers needed. With the single-wafer-based BUT structure, the thermopile consisting of 21 pairs of single-crystalline Si/Al thermocouples that show significantly higher Seebeck coefficient and lower noise compared to the traditional poly-Si/Al thermocouples is employed to construct the gas flow sensor, and the fabricated sensor chip size is as small as 0.65 mm×0.65 mm that facilitates low-cost high-throughput IC-foundry batch fabrication. The fabricated sensor shows a high normalized sensitivity of 199 μV/(SLM)/mW for nitrogen gas flow, which is 1 order of magnitude higher than that of the reported thermopile-based gas flow sensor, and a short response time of 3.5 ms could be achieved. With the new technique, the proposed sensors are promising in automotive and process control system applications.