Mittuniversitetet

In this paper we present the development and characterization of thermopile detector on a 4 mum thin self-supporting membrane made of the epoxy based photoresist SU-8. The membrane is realized using silicon bulk micromachining techniques. In many existing thermopile detectors, a temperature difference over the thermocouple junctions is achieved by connecting a thin membrane of either Si or Si₃N₄ to a silicon bulk. These materials suffer from relatively high thermal conductivity, which lowers the sensitivity of the detector. A material such as SU-8 has much lower thermal conductivity and is applied using standard photolithographic processing steps. Simulation results are presented which verifies SU-8 as a better choice than Si and Si₃N₄ when used as thermal insulating membrane in a thermopile detector. A thermopile consisting of 196 series coupled Ti/Ni thermocouples has been fabricated. Results from measurements are presented, showing a sensitivity of 5.6 V/W and a noise equivalent power (NEP) of 9.9 nW/radicHz.

This article present the fabrication and development of a thin metal film bolometer IR detector connected in a Wheatstone bridge configuration. The bolometer is constructed on a 4 μm thin self-supported SU-8 2002 membrane. A polymer material such as SU-8 has low thermal conductivity and is applied using standard photolithographic processing step, and this could increase detector sensitivity and lower the production cost. Thermal simulation results are presented, which verifies SU-8 as a better choice of materials compared to common membrane materials such as Si and Silicon nitride. Measurements on the fabricated nickel resistance bolometer on SU-8 2002 membrane show a sensitivity of 9.3 V/W when radiated by an IR laser with a wavelength of 1.56 μm.

Position-sensitive detectors (PSDs) are widely used in noncontact measurement systems. In order to minimize the size of such systems, interest has increased in mounting the PSD chip directly onto printed circuit boards (PCBs). Stress may be induced in the PSD because of the large differences in thermal expansion coefficients, as well as the long-term geometrical stability of the chip packaging. Mechanical stress has previously been shown to have an effect on the performance of semiconductors. The accuracy, or linearity, of a lateral effect PSD is largely dependent on the homogeneity of the resistive layer. Variations of the resistivity over the active area of the PSD will result in an uneven distribution of photo-generated current, and hence an error in the readout position. In this work experiments were performed to investigate the influence of anisotropic mechanical stress in terms of nonlinearity. PSD chips of 60×3 mm active area were subjected, respectively, to different amounts of compressive and tensile stress to determine the influence on the linearity.

Position sensing detectors (PSDs) are useful in many applications such as vibration, displacement and triangulation measurements. In this paper we have constructed a novel structure, which has higher inter-electrode resistance than a lateral effect PSD and is more robust to atmospheric turbulence than a conventional four-quadrant PSD (Nuclear Instruments and Methods in Physics Research A 466 (2001) 183). The detector structure is useful for applications with detector windows less than 0.5 x 0.5 mm(2), but the nonlinearity is the main concern for a detector of that size. Without any corrections for non-linearity the standard deviation of the error is 9 mum (2.2%). Using a simple analytical expression and a 2-d correction-function stored in a look-up table the positioning error is reduced to 6 (1.5%) and 2 (0.5%) mum, respectively.