Introduction
Before the invention of the electronic gas sensor in the 1920s, people relied on primitive and dangerous methods. These include canaries to detect low oxygen environments in mines, and flame lights to detect methane and oxygen levels. The replacement of these methods with electronic sensors has increased both the safety and reliability of gas detection. In addition, a wider variety of gases can be sensed and quantified. Despite these improvements, issues with sensors persist. Selectivity, the ability to differentiate between gases, proves a challenge, as do sensitivity to small gas concentration, repeat measurement stability, and cost. One possible way to compete with these challenges may be the carbon nanotube (CNT) transistor. These transistors are built on a layer of carbon nanotubes deposited on a silicon substrate. It is possible for gas molecules to adhere to the carbon nanotubes, thereby changing the conductivity of the nanotube. Repeated use of this sensor is possible with the use of heat or UV light to remove bonded gas particles. We set out to design an enclosure in which to test the changes in electrical properties of CNT transistors induced by the introduction of various gases into the chamber. An environmental test chamber was designed, and two field effect carbon nanotube transistors were created with which to test the chamber. The design considerations for the test chamber and transistors along with the fabrication will be discussed in this paper. Enclosure Design Certain considerations were taken into account when designing the test chamber. …show more content…
The unit needed to be airtight, transparent, and mostly nonreactive to allow for a wide variety of allowed substances. In choosing the material, we had to take into account the gasses that would be used, along with material properties regarding UV light transmission. Acrylic was the decided upon material satisfying the testing needs. The height requirements were set first, due to height restrictions of the microprobe station. The width and length were determined based off the dimensions of the transistor wafer. After much consideration, it was decided to make the housing a drawer to assist with reusability, safety, and ease of use. The drawer height was initially designed to house a small heater underneath allowing future testing. The design was drawn on AutoCAD, as shown in Figure 1. Figure 1. This figure shows the AutoCAD drawing of the environmental test chamber. As seen, the box slides out allowing wafer placement. …show more content…
The holes seen on the drawer face are for the gas and electrical connections. There is an input and output connection for the gas on opposite box sides. The electrical system requires 5 connections; 3 to gate voltage, 1 to source voltage, 1 to drain voltage. The holes are designed for typical banana plug attachments, enabling ease of use. Inside the box, the banana plug would be connected via clip to the board. When the clip is attached to the wafer, it in turns clamps it down to the drawer. This method would apply to the drain and source voltage. To connect to the gate voltage, the thinner silicon oxide layer on the bottom of the wafer would be scratched off and a rough metal would be placed on the drawer surface allowing electrical connection. This metal would be soldered to a wire and connected to the banana plug attachment. These connections allow for easy use and reusability. Enclosure Fabrication The enclosure was to be cut out using the laser cutter located in the Engineering Physics Lab in EGH. Due to excessive usage by other students and power supply failure, there was difficulty finding a time for machine usage. The testing chamber was unable to be cut and assembled, but will be completed the following semester by continuing students. Transistor Design For testing purposes, two CNT transistor substrates were designed. The designed transistors are similar to those designed by Eric Snow and F. Perkins in their 2005 paper “Capacitance and Conductance of Single-Walled Carbon Nanotubes in the Presence of Chemical Vapors”. Field effect transistors (FETs) were designed, which operate by applying a voltage to the transistor gate that allows a current to flow between the source and drain. The photolithography masks were designed in AutoCAD. Each wafer contains three separate transistors in order to test reproducibility, overcome the possibility of unusable transistors, and allow multiple measurements to be taken. The goal for the transistors was to have
Before the invention of the electronic gas sensor in the 1920s, people relied on primitive and dangerous methods. These include canaries to detect low oxygen environments in mines, and flame lights to detect methane and oxygen levels. The replacement of these methods with electronic sensors has increased both the safety and reliability of gas detection. In addition, a wider variety of gases can be sensed and quantified. Despite these improvements, issues with sensors persist. Selectivity, the ability to differentiate between gases, proves a challenge, as do sensitivity to small gas concentration, repeat measurement stability, and cost. One possible way to compete with these challenges may be the carbon nanotube (CNT) transistor. These transistors are built on a layer of carbon nanotubes deposited on a silicon substrate. It is possible for gas molecules to adhere to the carbon nanotubes, thereby changing the conductivity of the nanotube. Repeated use of this sensor is possible with the use of heat or UV light to remove bonded gas particles. We set out to design an enclosure in which to test the changes in electrical properties of CNT transistors induced by the introduction of various gases into the chamber. An environmental test chamber was designed, and two field effect carbon nanotube transistors were created with which to test the chamber. The design considerations for the test chamber and transistors along with the fabrication will be discussed in this paper. Enclosure Design Certain considerations were taken into account when designing the test chamber. …show more content…
The unit needed to be airtight, transparent, and mostly nonreactive to allow for a wide variety of allowed substances. In choosing the material, we had to take into account the gasses that would be used, along with material properties regarding UV light transmission. Acrylic was the decided upon material satisfying the testing needs. The height requirements were set first, due to height restrictions of the microprobe station. The width and length were determined based off the dimensions of the transistor wafer. After much consideration, it was decided to make the housing a drawer to assist with reusability, safety, and ease of use. The drawer height was initially designed to house a small heater underneath allowing future testing. The design was drawn on AutoCAD, as shown in Figure 1. Figure 1. This figure shows the AutoCAD drawing of the environmental test chamber. As seen, the box slides out allowing wafer placement. …show more content…
The holes seen on the drawer face are for the gas and electrical connections. There is an input and output connection for the gas on opposite box sides. The electrical system requires 5 connections; 3 to gate voltage, 1 to source voltage, 1 to drain voltage. The holes are designed for typical banana plug attachments, enabling ease of use. Inside the box, the banana plug would be connected via clip to the board. When the clip is attached to the wafer, it in turns clamps it down to the drawer. This method would apply to the drain and source voltage. To connect to the gate voltage, the thinner silicon oxide layer on the bottom of the wafer would be scratched off and a rough metal would be placed on the drawer surface allowing electrical connection. This metal would be soldered to a wire and connected to the banana plug attachment. These connections allow for easy use and reusability. Enclosure Fabrication The enclosure was to be cut out using the laser cutter located in the Engineering Physics Lab in EGH. Due to excessive usage by other students and power supply failure, there was difficulty finding a time for machine usage. The testing chamber was unable to be cut and assembled, but will be completed the following semester by continuing students. Transistor Design For testing purposes, two CNT transistor substrates were designed. The designed transistors are similar to those designed by Eric Snow and F. Perkins in their 2005 paper “Capacitance and Conductance of Single-Walled Carbon Nanotubes in the Presence of Chemical Vapors”. Field effect transistors (FETs) were designed, which operate by applying a voltage to the transistor gate that allows a current to flow between the source and drain. The photolithography masks were designed in AutoCAD. Each wafer contains three separate transistors in order to test reproducibility, overcome the possibility of unusable transistors, and allow multiple measurements to be taken. The goal for the transistors was to have