R. Rubio

Feasibility of a flip chip approach to integrate an IR filter and an IR detector in a future gas detection cell

In this work we have studied the feasibility of integrating an infrared filter and an infrared detector by means of a flip-chip technique. This filter and detector combination should be the heart of a future gas detection cell based on infrared absorption. In our case the filter is a surface micromachined Fabry-Perot interferometer, and the infrared detector is a bulk micromachined thermopile. The flip-chip technique is an elegant solution to assure the optical micro-alignment of both devices and allows the electrical contact needed to actuate active optical filters.

A highly sensitive IR-optical sensor for ethylene-monitoring

Precise and continuous ethylene detection is needed in various fruit storage applications. The aim of this work is the development of a miniaturised mid-infrared filter spectrometer for ethylene detection at 10.6 μm wavelength. For this reason optical components and signal processing electronics need to be developed, tested and integrated in a compact measurement system. The present article describes the proposed system set-up, the status of the development of component prototypes and results of gas measurements performed using a first system set-up. Next to a microstructured IR-emitter, a miniaturised multi-reflection cell and a thermopile-array with integrated optical filters and microstructured Fresnel lenses for the measurement of ethylene, two interfering gases and one reference channel are proposed. Recently a miniaturised White cell as absorption path is tested with various commercial and a self-developed thermal emitter. First ethylene measurements have been performed with commercial twofold thermopile detectors and a Lock-in-amplifier. These showed significant absorption at an ethylene concentration of 100ppm. For the detection module different types of thermopiles were tested, first prototypes of Fresnel lenses have been fabricated and characterised and the parameters of the optical filters were specified. Furthermore a compact system electronics for signal processing containing a preamplification stage and Lock-in-technique is in development.

A compact optical ethylene monitoring system

In various fruit storage applications precise and continuous ethylene detection is needed. The aim of this work is the development of a miniaturised mid-infrared filter spectrometer for ethylene detection at 10.6 &mgr;m wavelength. For this reason optical components and signal processing electronics were developed, tested and integrated in a compact measurement system. The present article describes the optical components, the integration of the optical system, electronics and results of gas measurements. Next to a Silicon-based macroporous IR-emitter, a miniaturised absorption cell and a detector module for the simultaneous measurement at four channels for ethylene, two interfering gases and the reference signal were integrated in the optical system. Optical filters were attached to fourfold thermopile-arrays by flip-chip- technology. Silicon-based Fresnel multilenses were processed and attached to the cap of the detector housing. Because of the high reflection losses at the silicon-air surface the Fresnel lenses were coated with Antireflection layers made of Zinc sulphide. For the signal processing electronics a preamplification stage and a Lock-in-board has been developed. First ethylene measurements with the optical system with miniaturised gas cell, Silicon-based IR-emitter, a commercial thermopile detector and the self-developed system electronics showed a detection limit of smaller than 20ppm.

Thermopile sensor array for an electronic nose integrated non-selective NDIR gas detection system

The fabrication and characterization of a thermopile sensor array is described in this work. The device is intended to be part of a non-dispersive infrared (NDIR) gas detection system integrated in an electronic nose where each sensor is not oriented for the detection of a particular substance. Different designs were considered changing the size of the array (9 or 16 elements) and improving some specific detector performance parameters: responsivity and noise equivalent power (NEP). After device fabrication, the measurements of these parameters show a good agreement with the thermal one-dimensional model used for the design.

Microsystems for the agrofood field

Microsystems will play an important role in the agrofood field as many different safety and quality assurance procedures may benefit from the inherent advantages of small, fast and reliable devices. An example is proposed for the detection of gases of interest in the control of fruit with a microsystem that combines optical and semiconductor gas sensors. A simple process step is also introduced that allows to improve the performances of such devices.

Optical simulation of a MOEMS based tuneable Fabry-Perot interferometer

Simulation of the optical response for a tuneable Fabry-Perot interferometer fabricated using silicon MOEMS (micro-opto-electromechanical system) technology is presented. This device, which is intended to be part of an NDIR (nondispersive infrared) system, is composed of two dielectric parallel mirrors; the upper mirror is a suspended structure, electrostatically actuated, that allows tuning of the length of the resonant cavity, and therefore selection of the wavelength region corresponding to a particular absorption band. As the final spectrum of the device is directly related to the planarity of the upper mirror, once validated with measurements in small areas of the surface of the device, the optical model is used to predict the response of the whole area of the interferometer. This allows us to estimate the effect of the planarity of the device on the resulting spectra.

Design and Fabrication of Micromachined Silicon Based Mid Infrared Multilenses for Gas Sensing Applications

To improve the sensitivity of a non-dispersive infrared optical gas sensor, diffractive Fresnel lenses have been designed, fabricated and tested. The target gases determine the wavelengths for the lens design: 10.6 mum, 9.7 mum, 3.5 mum, and 3.9 mum for ethylene, ammonia, ethanol, and the reference band; respectively. Four lenses have been fabricated on the same silicon substrate using reactive ion etching. In order to reduce the number of photolithographic processes, a new design based on sharing sixteen quantization steps through the four lenses is done. Finally, the test of the fabricated device is presented.

Influence of the doping material on the benzene detection

In this paper we describe the fabrication of low-cost micro-hotplate benzene sensors by using screen-printing technology. Sensitive layers of tin and tungsten oxide (pure and doped with 1% in weight of Au, Pt and Pd) were deposited on silicon micromachined substrates with low thermal inertia. Gas measurements were performed with the fabricated sensors and the results confirm the viability of the techniques introduced to obtain micromachined sensors suitable for battery-powered gas/vapour monitors

Towards a Microtechnology based 4-channel infrared detector unit for a miniaturised NDIR system

An infrared detector unit to be included in a miniaturised nondispersive infrared system (NDIR) is being developed with the aid of different microtechnologies: CMOS technology, silicon bulk micromachining and flip-chip techniques. The chosen application for this optical gas sensing approach is the storage ambient control of climacteric fruit such as apples. For this application the detection of different gases is of interest; ammonia (as a result of leaks of the cooling system), ethylene (as a monitor of the ripeness state of the fruit), and acetaldehyde or ethanol (as a measure of fruit stress)