This paper presents a monolithic 4 × 4 tin oxide gas sensor array together with on-chip multiplexing and differential read-out circuitry. A robust fabrication process focusing on the integration of the CMOS circuitry and the microelectromechanical systems (MEMS) structure is first described. The gas sensor uses a surface micro-machined micro-hotplate based structure. Platinum is selected as the material of choice for both the micro heater and the sensor’s electrodes, for its good thermal stability and compatibility with the sensing film. Different post-treatments are used to modify the characteristics of the tin oxide gas sensors hence improving the sensor’s selectivity of the overall sensor array. Furthermore, in contrast to the conventional voltage divider read-out technique, a novel differential read-out circuit (DRC) for tin oxide gas sensors is proposed. The DRC applies a constant current to drive the sensor and uses a unit-gain single stage amplifier (inverter) to generate a fully differential output, directly from the voltage drop across the sensor. The output of the DRC is simply proportional to the difference between the voltage on the two electrodes of the sensor but not to the transistor parameters such as mobility and threshold voltage, neither to the supply voltage. The monolithic sensor array and its pre-processing circuitry have been implemented in our in-house 5 μm process. Experimental results showed good linearity at the output of the DRC for a wide range of sensor resistance variation (over 20 MΩ). The fabricated micro-hotplate sensor array was tested for four target gases. Results show good sensitivity and interesting thermal characteristic leading to only 15.5 mW power consumption for 300 °C operating temperature.

A monolithic integrated 4 × 4 tin oxide gas sensor array with on-chip multiplexing and differential readout circuits

Synthesis and acidic properties of the SiO2/SnO2 mixed oxides obtained by the sol–gel process. Evaluation of immobilized copper hexacyanoferrate as an electrochemical probe

This paper describes the fabrication process for a novel convex microhotplate (MHP) structure using surface micromachining technology. The process is used to fabricate an integrated 4times4 tin oxide gas sensor array. Surface micro-machining is selected for its simplified process and CMOS compatibility. However, limited sacrificial layer thickness usually leads to higher power consumption. In this work, a convex MHP structure is developed to increase the thermal efficiency, which is critical for large dimension and low-power gas sensor array integration. Before the structure release process, 700degC-950degC annealing process was carried out on the 190 times190 mum2 MHP with 2.8 mum polysilicon sacrificial layer. It is shown that higher annealing temperature leads to lower tensional stress of the MHP membrane and larger curvature of the released structure, which enables higher thermal efficiency. Among the four annealing temperatures, the 950degC annealed MHP has the largest curvature of 2.438 cm-1 and the highest thermal efficiency of 13degC/mW. Experimental results showing the responses of the sensor array to different combustible gases are also illustrated in this paper. Comparison of power consumption with other designs reported in the literature illustrates the effectiveness of the proposed process.

An Integrated Surface Micromachined Convex Microhotplate Structure for Tin Oxide Gas Sensor Array

The use of magnetic fields to control cathode spot location and motion and to collimate and direct the plasma flow in vacuum arc deposition apparatus is reviewed. Retrograde and acute angle motion are used to control the location and motion of cathode spots, in order to confine them to the cathode surface facing the substrates, to prevent local overheating, and to reduce macroparticle production. Axial fields are use to collimate cathode spot produced plasma jets and to bend them around macroparticle-occluding obstacles in filtered vacuum arc deposition. Advances have been made in understanding these phenomena, but theoretical models have not yet been formulated which can predict plasma behavior sufficiently well for apparatus design.

Magnetic control, in vacuum arc deposition - a review

Thermochromic Vanadium Oxide Coatings Grown by APCVD at Low Temperatures

Light refraction in a medium results from energy exchange between the medium and the magnetic field of the light. Formulas of refractive index, that is, the ratio of light speed in vacuum to light speed in the medium, were derived with the inductor model of electron cloud and the law of energy conservation. Refractive indices of several media were calculated using the formulas derived and the calculated results are in agreement with the results measured. The anisotropy and the nonlinearity of the refractive index are explained with the theory described in this work.

https://iopscience.iop.org/article/10.1088/1009-1963/13/8/032/pdf

Effect of magnetic field of light on refractive index

Modification of tin dioxide thin films by ion implantation

The performance and characteristics of a cathodic arc deposition apparatus consisting of a titanium cathode, an anode with and without a tungsten mesh, and a coil producing a focusing magnetic field between the anode and cathode are investigated. The arc voltage Va is measured with a fixed arc current. The relationship between Va and the magnetic field B with and without a mesh is obtained. In addition, the relationship between the arc current Ia and Vc, the voltage to which the artificial transmission line was charged, is measured with and without the mesh to determine the minimum ignition voltage for the arc. The arc resistance increases with the focusing magnetic strength B and decreases when using the mesh. Our results indicate that the high transparency and large area of the mesh allows a high plasma flux to penetrate the anode from the cathodic arc. The mesh also stabilizes the cathodic arc and gives better performance when used in concert with a focusing magnetic field. PACC: 5275; 5230; 5280; 2925

The effect of mesh anode on cathodic arc in focusing magnetic field

A Monte Carlo computer simulation code has been developed to describe the behavior of incident particles and the growth of (TiMo) N films in the multicomponent ion beam enhanced deposition process, which combines bombardment with a multicomponent ion beam of N + +Mo + and sputter deposition of a Ti film. The film composition profile and intermixed layer between the substrate and the film were studied using a computer simulation method. It is shown that Mo ion implantation has a stronger mixing effect in the film–substrate interface than does N ion implantation. The N profile of the computer simulation conforms to that of the Auger electron spectroscopy results.

Computer simulation of multicomponent ion beam enhanced deposition of (TiMo) N films

The performance and characteristics of a cathodic arc plasma source, consisting of a titanium cathode, an anode with and without a tungsten mesh, and a coil producing a focusing magnetic field between the anode and cathode, are investigated. The high transparency and large area of the mesh allow a high plasma flux to penetrate the anode from the cathodic arc. The mesh helps to decrease the arc resistance and the ignition voltage of the cathodic arc in the focusing magnetic field, and to increase the life of the source, which means that the source makes the cathodic arc easily and greatly stabilized during the operation when a focusing magnetic field exists in the source.

http://iopscience.iop.org/article/10.1088/0256-307X/18/8/336/pdf

Zhang Tao

Papers

Effect of magnetic field of light on refractive index

Modification of tin dioxide thin films by ion implantation

The effect of mesh anode on cathodic arc in focusing magnetic field

Computer simulation of multicomponent ion beam enhanced deposition of (TiMo) N films

Assistant Anode in a Cathodic Arc Plasma Source