Field Emission Pressure Sensor Research Articles

Fabrication of a graphene-based pressure sensor by utilising field emission behavior of carbon nanotubes

In this paper, a miniature graphene-based field emission pressure sensor is reported for the first time, in which carbon nanotubes have been applied as the cathode and reduced graphene oxide sheets have been utilized as the flexible anode. Since, graphene is the thinnest (one atom thick) known structure with a uniform thickness, graphene based membrane is a promising candidate for pressure sensors which allows both high sensitivity and very small chip area, simultaneously. A maximum sensitivity of about 21.9μA/A/Pa is achieved at the bias voltage of 5 V for the fabricated field emission pressure sensor, which is about two orders of magnitude higher than the previously reported graphene based pressure sensors. The fabricated structure has been also used as a graphene based resonator in which emission current is applied to detect the mechanical resonance, efficiently. The measured resonance frequency is measured about 10 MHz, which is shifted to lower frequencies by increasing the ambient pressure. The measured sensitivity, for the resonant operation mode, is about 11.32 Hz/Pa (S = Δf/ΔP). Owing to the inherent low mass of graphene, the presented structure can be entitled as a promising resonant pressure sensor.

MEMS Carbon Nanotubes Field Emission Pressure Sensor With Simplified Design: Performance and Field Emission Properties Study

The pressure sensor application gained recently substantial interest in many fields of basic and applied research and applications. In this paper, microelectromechanical system (MEMS)-based pressure sensor contains nanostructured electrode consisting of carbon nanotube (CNT) array. CNTs are directly grown on such electrode by plasma-enhanced chemical vapor deposition method using microwave plasma torch at atmospheric pressure. This growth method enables us to use a simple electrode structure without need of buffer layer and time-consuming lithography process. Combination of CNTs field emission and MEMS membrane mechanical properties make possible to enhance sensitivity of the sensor. Field emission properties of CNTs are measured by newly developed system enabling us precise measurement of expecting properties, such as dependence on diaphragm (upper electrode) distance, applied voltage, and stability of the sensor. Measured values are compared with a numerical modeling of the membrane system in Coventor Ware software by finite-element method. We also suggest encapsulating the sensor using glass frit bonding because such method is more suitable for high vacuum requirements of the field emission operation.

High sensitive/wide dynamic range, field emission pressure sensor based on fully embedded CNTs

The formation of high sensitivity–wide dynamic range field emission pressure sensors based on carbon nanotubes (CNTs) is reported. In this work, CNTs are grown inside an array of micromachined holes in order to ensure a high sensitivity and a wide dynamic range by allowing anode–cathode proximity while preventing anode–cathode direct contact simultaneously. External pressure is applied to a Si-based flexible anode, which results in consequent variations in emission current, due to electric field changes. Microcavities in this structure have been formed by a Si deep vertical etching process, while the CNTs have been grown by direct current plasma-enhanced chemical vapour deposition. Also, it is demonstrated that a similar fabrication process can be applied to implement a device with an electrically controllable emission current. A high sensitivity of 1.5–13.7 µA kPa−1 (with Vanode/cathode < 100 V) within a dynamic range from around 0.1 to 1 GPa, is measured in this experiment.

Dynamic range and sensitivity of field emission pressure sensors with non-silicon membranes

We report on the dynamic range and sensitivity simulations of a functional field emission-based pressure sensor. The device comprises a titanium nitride membrane acting as the anode in front of a flat boron nitride cold cathode emitter. We previously reported the problem of non-linearity of these sensors and studied their performance for different membrane geometries and membranes using different materials such as Si, Ti, Ta, and TiN [N. Badi et al., Appl. Surf. Sci. 256 (2010) 4990–4994]. Of the materials investigated, TiN seems to have the most desirable characteristics with respect to linearity. In this paper we report on the effects of membrane dimensions on the sensor operation. Results show how a sensor having a TiN membrane of standard dimension can be tuned during operation to have maximum dynamic range without affecting the sensitivity. The membrane dimensions have a strong effect on the device dynamic range. Small portions of the entire range could however be selected by changing the device operating voltage. We also have shown that smaller area membranes result in devices with better response in terms of constant sensitivity, as compared to those with thicker membranes. The device can be operated over its entire dynamic range by tuning the operating voltage of the device to keep the sensitivity a constant.

Fabrication of highly sensitive field emission based pressure sensor, using CNTs grown on micro-machined substrate

Carbon nanotubes have been used as cold cathode emitter in the fabrication of a sensitive field emission pressure sensor. Vertically aligned carbon nanotubes were grown using the plasma-enhanced chemical vapor deposition (PECVD) on a micro-machined silicon substrate. A silicon membrane was used as the flexible anode against the fabricated CNT-based cathode. A 2-μm thick SiO2 layer has been applied as the anode–cathode spacer and the output results have been compared with a similar sensor with 120μm spacer. Results show that the sensitivity and the output emission current of the fabricated sensor have been highly improved by decreasing the anode–cathode spacing. Measurements show an ultra-high sensitivity of about 100–970μA/kPa which is higher than the similar pressure sensors. Low working voltage and high thermal stability of the fabricated sensor are among the other advantages of the presented sensor.

Field emission pressure sensors with non-silicon membranes

We report on the fabrication of cold cathode emitter and the design parameter simulation of a functional field emission-based pressure sensor. This device comprises a membrane made of metallic compound acting as the anode in front of a flat cold cathode emitter. First, the mechanical deflection of a diaphragm under selected input pressures is modeled. The current density distribution in the deflected diaphragm is then calculated using realistic field emission characteristics from fabricated sulfur doped boron nitride (S-BN) cold cathode device. The total current output was found by integrating the measured current density of the fabricated electron emitter device over the entire diaphragm area of the membrane as function of external pressure. The results show that conventional silicon membranes would pose problems when implemented in a real field emission device, and show how the use of unconventional materials (i.e., TiN) can help overcome these problems.

Studies on vacuum microelectronic pressure sensors based on carbon nanotubes arrays

A novel field emission pressure sensor has been achieved utilizing carbon nanotubes (CNTs) arrays as the electron source. The sensor consisted of the anode-sensing film fabricated by wet etching process and multi-wall carbon nanotubes (MWNTs) arrays cathode in the micro-vacuum chamber. MWNTs were grown on the silicon substrate by thermal CVD. The prototype pressure sensor had measured sensitivity of about 0.35–6.1 nA/Pa (5–550 KPa). The work suggests the potential use of CNTs-based field-emitter in microsensors such as accelerometers and tactile sensors.

Simulation and fabrication of carbon nanotubes field emission pressure sensors

A novel field emission pressure sensor has been achieved utilizing carbon nanotubes (CNTs) as the electron source. The sensor consists of the anode sensing film fabricated by wet etching process and multi-wall carbon nanotubes (MWNTs) cathode in the micro-vacuum chamber. MWNTs on the silicon substrate were grown by thermal CVD. The prototype pressure sensor has a measured sensitivity of about 0.17–0.77 nA/Pa (101–550 KPa). The work shows the potential use of CNTs-based field-emitter in microsensors, such as accelerometers and tactile sensors.

Research on carbon nanotube array field emission pressure sensors

A novel field emission pressure sensor has been achieved using carbon nanotube (CNT) arrays as the field emitters. The sensor consists of the anode elastic membrane fabricated by wet etching process and a multi-wall carbon nanotube array cathode in the micro-vacuum cavity. The prototype pressure sensor has a measured sensitivity of about 0.16-0.78 nA/Pa(101-550 kPa). The work suggests the potential use of CNT-based field emitters in microsensors such as accelerometers and tactile sensors.

Application of nano-crystalline silicon film in the fabrication of field-emission pressure sensor

A kind of filed-emission array pressure sensor is designed based on the quantum tunnel effect. The nano-crystalline silicon film is prepared by chemical vapor deposition (CVD) method, with the grain dimension and thickness of the film 3—9 nm and 30—40 nm, respectively. The nano-crystal-line silicon film is introduced into the cathode cones of the sensor, functioning as the essential emission part. The silicon nano phase is analyzed by HREM and TED, the microstructure of the single emitter and emitters array is inspected by SEM, and the field emission characteristics of the device are studied by an HP4145B transistor tester. The experimental results show that the measured current density emitted from the effective area of the sensor can reach 53.5 A/m 2 when the exterior electric field is 5.6×10 5 V/m.

Study of porous silicon, silicon carbide and DLC coated field emitters for pressure sensor application

This paper is a revue of our experimental data regarding field emitter array fabrication, various field emission materials and application in pressure sensors domain. Silicon emitter's arrays of different sizes and geometrical shapes were realised using micromachining technologies. Some important aspects as control in etch rate, emitter profile, selectivity and surface morphology were investigated. The emitter surface was modified or was covered by different materials in order to improve the emission properties. The most usual materials investigated for FED applications were: Si, diamond-like carbon layers, silicon carbide, and porous silicon. The main application which is present in our attention is the field emission pressure sensor.

Nano Crystalline Silicon Film Serves as the Emission Material for the Field Emission Pressure Sensor

AbstractThe prototype of a field-emission pressure sensor with a novel structure based on the quantum tunnel effect is designed and manufactured. Moreover the nano crystalline silicon film technology is introduced into the fabrication of the device effectively, which performs the function mostly as the field-emission material, the device field-emission characteristic of the nano silicon film is investigated, the experimental results show that the measured current density emitted from the effective area of the sensor can reach 53.5A/m2, when the exterior electric field is 5.6×105V/m.

Analysis of a pressure sensor based on an array of collector-assisted field-emission triodes

The purpose of this paper is to analyze the operation of a pressure sensor based on an array of collector-assisted field-emission triodes (FETs). The silicon membrane (the anode of the device) put in front of the array is bent by the external pressure, and thus, the field-emission current is modified. An analytical solution has been used to calculate the deflection of the silicon diaphragm when the pressure is applied and a numerical model was developed for the single emitter FET. The array emission current is obtained adding the contributions of all the FETs in the array, no interaction between the emitters being considered. The device sensitivity and resolution have been computed as functions of both the silicon membrane and FET array parameters. Better sensor sensitivity and resolution are obtained for those situations, which assure higher field-emission currents. A simple analytical model was developed for the field-emission pressure sensor, supporting these observations. The obtained modeling results can be further used for sensor design improvement.