Gas Pressure Sensor Based on PECVD Grown Carbon Nanotubes
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1018-EE14-05
Gas Pressure Sensor Based on PECVD Grown Carbon Nanotubes Richard Ficek1, Marek Elias2, Lenka Zajickova2, Ondrej Jasek2, and Radimir Vrba1 1 Department of Microelectronics, Brno University of Technology, Faculty of Electrical Engineering and Communication, Udolni 53, Brno, 602 00, Czech Republic 2 Department of Physical Electronics, Masaryk University, Faculty of Science, Kotlarska 2, Brno, 611 37, Czech Republic ABSTRACT In this paper the development and fabrication of the pressure sensor based on electron field emission from carbon nanotubes (CNTs) was described. The sensor consisted of two parts: a silicon membrane as an anode; and multi-walled CNTs on a silicon cathode, creating a vacuum micro-chamber. Both electrodes were fabricated from the silicon single crystal (Si) wafer of an orientation doped by phosphorus. The CNTs were grown by a plasma enhanced CVD using an iron catalyst in an atmospheric pressure microwave torch. The catalyst was patterned into an area corresponding to the membrane dimensions. The thin CNTs with a diameter of about 80 nm were standing vertically perpendicular to the substrate due to a crowding effect. In order to find the threshold current, the emission characteristics of prepared sensors were measured. INTRODUCTION Pressure sensors are very important microelectronic devices that can be based on several different principles [1,2,3]. One of them, the field emission vacuum sensor, has excellent temperature stability, low-power dissipation, resistant to radiation and quick responses. Up to now, devices utilizing electron emitters are mostly composed of arrayed silicon tips fabricated by an etching process [4]. Carbon nanotubes (CNTs) are, due to their unique properties, undoubtedly very promising material for many applications [5,6].The CNTs based field emitters exhibit low threshold voltage, high emission current density and good time stability of emission current [7,8,9]. In this paper, CNTs were used as a field emission source much like the surface increase element. FABRICATION OF PRESSURE SENSOR The manufactured pressure sensor is based on the fact that the field emission current is correlated with the electrical field strength, i.e. the anode-emitter distance when the applied voltage is fixed. External pressure acting on the sensor bends the anode membrane and the distance between the anode and emitting cathode changes accordingly. The sensor consists of three parts: silicon membrane as the anode; emitting CNTs on the silicon cathode; and an insulating rectangular spacer made of double-sided sticky tape. These parts create a vacuum micro-chamber of the sensor as shown below in figure 1. Both electrodes were fabricated from a single silicon crystal (Si) wafer of an orientation (100) doped by phosphorus to the specific resistance of 0.005 Ωcm. The wafer was relatively thick, 525 µm, in order to manufacture a sturdy vacuum chamber.
Sensor anode
Figure 1. Scheme of the field emission pressure sensor. The membrane area and its thickness were optimized by a numerical simu
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