Screen-Printed Ceramic MEMS for Metal Oxide Gas Sensor

Procedia Engineering, 2015

The application of MEMS technology for the fabrication of MOX sensors with low power consumption becomes now a very important trend in gas sensor design. However, traditional silicon technology has some evident disadvantages, when applied in high-temperature devices produced in limited batch. We present our attempt to combine the advantages of ceramic MEMS technology (high working (600ºC) and technological treatment (1000ºC) temperature, chemical stability at high temperature) with the advantages of additive technologies for the fabrication of functional elements of gas sensor (heaters, sensing, and catalytic layers). We developed conductive silver, gold and platinum nanoparticle (10-30 nm) inks usable in ink and aerosol jet printers and demonstrated the possibility to fabricate narrow conductive lines of microheaters and electrodes of sensor (line width 35 m). The combination of jet printing onto thin ceramic substrate with laser cutting enables the fabrication of advanced cantilever type sensors operating in pulsing heating mode.

Sensors, 2007

In this paper, the reliability of a micro-electro-mechanical system (MEMS)-based gas sensor has been investigated using Three Dimensional (3D) coupled multiphysics Finite Element (FE) analysis. The coupled field analysis involved a two-way sequential electrothermal fields coupling and a one-way sequential thermal-structural fields coupling. An automated substructuring code was developed to reduce the computational cost involved in simulating this complicated coupled multiphysics FE analysis by up to 76 percent. The substructured multiphysics model was then used to conduct a parametric study of the MEMS-based gas sensor performance in response to the variations expected in the thermal and mechanical characteristics of thin films layers composing the sensing MEMS device generated at various stages of the microfabrication process. Whenever possible, the appropriate deposition variables were correlated in the current work to the design parameters, with good accuracy, for optimum operation conditions of the gas sensor. This is used to establish a set of design rules, using linear and nonlinear empirical relations, which can be utilized in real-time at the design and development decision-making stages of similar gas sensors to enable the microfabrication of these sensors with reliable operation.

2006

Technical challenges for developing micro sensors for Ultra High Temperature and turbine applications lie in that the sensors have to survive extremely harsh working conditions that exist when converting fuel to energy. These conditions include high temperatures (500-1500°C), elevated pressures (200-400 psi), pressure oscillations, corrosive environments (oxidizing conditions, gaseous alkali, and water vapors), surface coating or fouling, and high particulate loading. Several technologies are currently underdeveloped for measuring these parameters in turbine engines. One of them is an optical-based non-contact technology.

Thin Solid Films, 2001

A novel prototype of low-power thick-film gas sensor deposited by screen-printing onto a micromachined hotplate is presented. The micro-heater is designed to maintain a film temperature of 400ЊC with less than 30 mW of input power. The fabrication process involves a combination of standard, VLSI-compatible, micromachining procedures and computer-aided screen-printing. A dielectric membrane of Si N and SiO has been obtained with an embedded poly-Si resistor acting as a heating element. The 3 4 2 bonding pad and contacts have been realised by a TirTiNrCrrAu structure and the sensing film has been deposited by a screen-printing technique. Here follows a characterisation of a device, based on SnO sensing film, at working conditions 2 together with the response curve for CH and NO . We will also address some important improvements to the micro-hotplate 4 2 structure, which leads to an increased flexibility of the device. ᮊ

Journal of Nanoparticle Research, 2006

This article gives an overview on recent developments in metal-oxide-based gas sensor systems, in particular on nanocrystalline oxide materials deposited on modern, state-of-the-art sensor platforms fabricated in microtechnology. First, metal-oxide-based gas sensors are introduced, and the underlying principles and fundamentals of the gas sensing process are laid out. In the second part, the different deposition methods, such as evaporation, sputtering, sol-gel techniques, aerosol methods, and screen-printing, and their applicability to micro-scale substrates are discussed in terms of their deposition precision, the achievable layer thickness, as well as with regard to the possibility to use pre-processed materials. In the third part, microsensor platforms and, in particular, semiconductor-and microelectronics-based sensor platforms, which have been fabricated in, e.g., standard CMOS-technology (CMOS: complementary metal-oxide semiconductor), are briefly reviewed. The use of such microfabricated sensor platforms inevitably imposes constraints, such as temperature limits, on the applied nanomaterial processing and deposition methods. These limitations are discussed and work-arounds are described. Additionally, monolithic sensor systems are presented that combine microtransducers or microhotplates, which are coated with nanomaterials, with the necessary control and driving electronics on a single chip. The most advanced of such systems are standalone units that can be directly connected to a computer via a digital interface. There are currently several companies that market metal-oxide-based gas sensors, for example Figaro (www.figarosensor.com), FIS (www.fisinc.co.jp), Microchemical Systems, MICS (www.microchemical.com), City Technology (www.citytech.com), AppliedSensor (www.appliedsensor.com), Umwelt sensortechnik GmbH, UST (www.umweltsensortechnik.de), and Paragon (www.paragon-online1.de). Metal-oxide-based gas sensors more and more penetrate also mass-market applications, which include, e.g., automotive applications (cabin air

Sensors and Actuators B: Chemical, 2001

We report on the design, implementation and characterisation of a thick-®lm gas sensor deposited for the ®rst time by screen-printing technique onto a micromachined hotplate, the microheater maintains a ®lm temperature as high as 4008C with <30 mW of input power. The microheater consists of a dielectric stacked membrane equipped with embedded polysilicon resistors acting as heating element as well as temperature sensing elements. Extensive ®nite-element computer simulations were carried out during the design step to optimise the radial temperature gradient up to 12008C/mm. A newly developed scheme for temperature measurement was adopted for on-line adjustment of the ®lm temperature through a conventional low-power proportional integral (PI) regulator. Deposition of sensing layers based on semiconductor oxides, such as SnO 2 was achieved by computer-aided screen-printing. The ®lms were then ®red through the microheater itself to guarantee thermodynamic stability for long time exploitation. The response of the device to CO, CH 4 and NO 2 at concentrations typical for indoor and outdoor applications was recorded by measuring the ®lm resistance through ultra high impedance CMOS circuit.

MRS Proceedings, 2004

ABSTRACTIn this work we employed lithographic techniques, combined with sputtering depositions, to fabricate semiconductor metal-oxide (MOX) gas sensors with controlled grain dimensions. The basic idea is to replace the continuous sensing film of standard MOX sensors with a pattern of wires in the sub-micron scale, thus controlling the lateral size of the grains. Regarding the fabrication process, we followed two different approaches: a plain lift-off technique and a substrate patterning process. We present a comparison between the results of both the approaches. Furthermore, we tested the electrical responses to several gases and compared them with those of continuous film sensors. The experimental data highlight an improvement for the patterned sensors.

Advanced Materials, 2001

Experimental ITO-coated glass was used as the substrate for the OLEDs, and was subjected to a routine cleaning procedure prior to loading into an evaporator [17]. Tris-(8-hydroxyquinoline) aluminum (Alq) and a-naphthylphenylbiphenyl diamine (NPB) were employed as the electron-transporting/emissive layer and hole-transporting layer, respectively. A multilayer structure of NPB (75 nm)/ Alq (75 nm)/LiF (0.3 nm)/Al (0.6 nm) was sequentially deposited on the substrate by resistive heating. Then, a 90 nm thick zinc oxide film was evaporated onto the multilayer structure in an O 2 ambience of 1 10 ±4 torr and followed by a 100 nm thick Al film. In some cases, calcium boride was utilized as an absorbing material to form the device with a configuration of NPB (75 nm)/Alq (75 nm)/calcium boride (90 nm)/Al (100 nm). Both zinc oxide and calcium boride were evaporated by electron beams. The substrate temperature during deposition was estimated to be in the range of 50±60 C. In the e-beam deposition, a magnetic field was applied across the substrate to repel electrons and ions, thus ensuring no radiation damage to the OLED layer structure, particularly the underlying Alq layer, occurred during the deposition [6,7]. A control device was also made with a configuration of ITO/NPB (75 nm)/Alq (75 nm)/ LiF(0.3 nm)/Al (100 nm). Device preparation was completed with encapsulation in a dry argon glove box.

Researches on microcantilever MEMS are numerous in different areas, physical or chemical sensing, actuation or energy harvesting. Because of their high sensitivity at room temperature, they have been shown to be interesting for gas detection. Though silicon technology allows the processing of such cantilevers, alternative technologies are also attractive and have been developed for a few years. Potential achievement of organic and inorganic thick-film cantilevers is studied, through the association of the sacrificial layer process to the wellknown screen-printing technology used for the fabrication of low cost components and microsystems. Epoxytype, gold and resonant piezoelectric Au/PZT/Au cantilevers with or without coating have been successfully tested under humidity, toluene and benzene. The potentiality of the screen-printing technology for the development of cantilever-based gas sensors is demonstrated.

Microsystem Technologies, 2008

Functional micro-and nanosized metal oxide thin film structures are very promising candidate for future gas-sensors. Their reduced size offers an increased surface to volume ratio thus improving sensitivity and sensor performance. Whilst most experimental nanostructures are produced using a bottom-up approach, a top-down sputtering technique for structuring nano-sized gas sensitive metal oxide areas is presented in this letter. Oxidised silicon wafers were used as substrates. The silicon dioxide film of 1 lm thickness was prepared by thermal oxidation in order to insulate the gas sensing elements from the substrate. The sensor chips had an overall size of (1.5 9 1.5) mm 2 onto which a Ta/Pt film (20/200 nm thickness) was deposited and patterned to act as electrodes, heater and temperature sensor. In a second step micro-scaled tin dioxide layers (60 nm thick, 5 lm width) were deposited by sputtering techniques and photolithographical patterning between the platinum micro-electrodes (4 lm gap). Finally, the width of the stripes was reduced using focused ion beam technology to obtain the desired size and structure. This enables the control of the dimensions of the structures down to the resolution limit of the FIB-system which is about 10 nm. The structural and electrical characterisation of the sensors and their responses during exposure to several test gases including O 2 , CO, NO 2 and H 2 O are presented as well.