This paper reports the first SOI smart temperature sensor operating up to 250°C by integrating on the same chip the solid-state sensor itself (a SOI lateral PIN diode) and a simple digital conversion circuit. The sensor is implemented in a Fully-Depleted Silicon-On-Insulator process featuring a film thickness of 80nm [1]. Using the extraction method presented in [2], our non-gated PIN diode presents a quasi-linear temperature voltage characteristic when biased at a constant current (figure 1). The digital conversion circuit is shown in figure 2. The sensor output (figure 3) is the ratio of the time periods counted for the voltage on a reference capacitor charged by a constant current to reach respectively V_D (diode voltage) and V_REF (a Ultra-Low-Power reference voltage stable with temperature [3]) : α = T_D / T_REF

The total power consumption of the circuit is 50µA*3V=150µW only. Despite the non-linearity of V_REF , which is quite stable up to 200°C, the accuracy is 3°C in the range 25°C-250°C with 2 calibrations points (25°C, 200°C). For a fully-calibrated sensor, the maximum accuracy is 2°C with a resolution of 0.8°C.

[1] D. Flandre et al.,“Fully-depleted SOI CMOS technology for heterogeneous micropower, high-temperature or RF microsystems”, Solid-State Electronics, -vol. 45, pp. 541–549, February 2001.

[2] S. Adriaensen, D. Flandre, “High-Temperature Accurate Characterisation of SOI Bipolar/Diode Devices for their applications in Precise High-Order Bandgap References”, HITEN’03, Oxford, UK.

[3] S. Adriaensen, V. Dessard, D. Flandre, “25 to 300°C ultra-low-power voltage reference compatible with standard SOI CMOS process”, Electronics Letters, vol. 38, issue 19, pp. 1103-1104, September 2002.

Figure 1. Analog to Digital Converter.

Figure 2. VD-T curve of a SOI non-gated PIN diode (W=758μm, L=5μm) for ID=2μA.

Figure 3. Sensor output and accuracy for different calibrations.

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