A.W. van Herwaarden

Integrated thermopile sensors

Abstract This paper is about integrated silicon thermopiles and their applications in silicon sensors. After a short description of the thermoelectric effect and its use in silicon thermopiles, some attention is devoted to the design of micromachined structures for implementing thermal sensors. The various sensing principles based on thermal effects are discussed next. Finally, an impression is given of some of the recently developed silicon-thermopile sensors which implement these sensing principles.

High-sensivity 2-D flow sensor with an etched thermal isolation structure

Abstract This paper describes a two-dimensional thermal flow sensor, fabricated by silicon planar technology and subsequent micromachining. Using a two-step etching process, a thermally isolated floating-membrane structure has been formed in the chip. Flow is measured by detecting flow-induced temperature differences in two directions on the heated membrane, and this principle allows directional flow measurements over the full range of 360°. When compared to a wafer-thick silicon flow sensor of similar dimensions, this new structure possesses a much higher sensitivity, and an improved offset and time response behaviour. The response time for the behaviour of the average membrane temperature is found to be of the order of 150 ms, while for the temperature-difference measurement mode the response time is estimated to be only 14 ms. First experiments show a typical error of 3° in predicted flow angle, and 5% in flow velocity.

Liquid and gas micro-calorimeters for (bio)chemical measurements

Abstract Micro-calorimeters are offsetless and often highly selective chemical sensors that measure concentrations of substances in gases and liquids by detecting the heat of reaction. In this paper we present the results of a comprehensive study of the design, operation and performance of integrated-silicon and poly-silicon micro-calorimeters for use with enzymatic and electropolymerized reactive coatings.

Small-size vacuum sensors based on silicon thermopiles

Abstract This paper describes the development of integrated silicon thermal vacuum sensors with much reduced sizes, compared with previously described versions. After a short expose of the physics of thermal vacuum measurement, the general sensor structure is elucidated. Then the novel structure is described, seven times smaller but three times more sensitive than previous versions. The experimental results show a sensitivity of 12.4%/Pa for nitrogen and a pressure range of 1 mPa to 10 kPa absolute pressure. The sensor can be mounted in a small TO-5 housing.

A silicon-silicon nitride membrane fabrication process for smart thermal sensors

Abstract A new structure consisting of a silicon membrane suspended in a nitride membrane has been realized. This structure combines the advantages of the high thermal isolation of nitride membranes and the use of bipolar devices as sensing elements. The nitride membrane and the silicon membrane are fabricated within a single etch step. The process and its options are described by a design that includes several mono-Si thermopiles in a 2.5 μm thick silicon membrane and poly-Si thermopiles resting on a 0.3–0.8 μm thick oxide/nitride membrane. In all cases diodes, transistors and heating resistors are integrated as well. To prove the versatility of this process, as well as to,indicate which thermal configuration is more suitable for a specific application, a number of sensors realized with.this process will be briefly described.

Design and fabrication of infrared detector arrays for satellite attitude control

Abstract This paper describes the design, modelling and fabrication of infrared detectors for attitude control systems (ACS) for satellites. After a short introduction on the use and control of satellites in general, we explain the advantages of our integrated arrays of infrared detector units (pixels). Two types of detectors have been manufactured, a staggered array (ISA) with 32 pixels (in two staggered arrays of 16 pixels each) or in a cross of four staggered arrays (FPA) having 128 pixels in total. The choice depends upon the specific application (geostationairy or GEO orbit or low-altitude orbit). The detectors are based on a bipolar silicon process for the mechanical structure (electrochemically controlled etching (ECE)-KOH etching), with a SiN membrane for thermal isolation of the pixels, which have a polymer black coating for transduction of radiation to heat and n-type vs. p-type polysilicon thermopiles for heat detection. The pixel pitch is 600 μm, the black area is about 495×440 μm and the pixel sensitivity is about 55 V/W, at a thermopile resistance of 23.5 kΩ. The ISA measures in its present form 13.5×4 mm, the FPA measures 20.5×20.5 mm.

Thermogravimetric device with integrated thermal actuators

This paper presents the first MEMS device for ThermoGravimetric Analysis (TGA) with integrated thermal actuators. It consists of a sensing cantilever paddle connected to two separated thermal actuators, one at each side of the cantilever. Moreover, it has an integrated thermocouple that allows combined TGA and calorimetric measurements. To demonstrate the device performance TGA of copper sulfate pentahydrate (CuSO4·5H2O) samples has been performed. The operation range for the TGA device is 40 pg up to 0.1 µg for the mass and 25 up to 650 °C for the temperature. The mass sensitivity is about 200 Hz for a 1 ng sample on the 10 kHz resonance frequency.