Technology Advances
- PDF / 1,817,809 Bytes
- 3 Pages / 612 x 792 pts (letter) Page_size
- 58 Downloads / 170 Views
TECHNOLOGY ADVANCES
Microfabricated Gas Sensors Detect Hydrogen over Wide Range of Concentrations Leak detection and monitoring of flammable or explosive concentrations of gas for safe use, storage, and handling are among the potential industrial applications for the high-temperature hydrogen gas sensors developed by NASA Glenn Research Center in conjunction with the Electronics Design Center at Case Western Reserve University. The sensors are microfabricated and micromachined using microelectromechanical-systems-based technology to minimize size, weight, and power consumption. The sensor technology development also depends on the use of nanomaterials and silicon carbide (SiC) as an electronic semiconductor. Microfabricated sensors are small and lightweight, and consume minimal power. Compared with conventional sensors, these devices often have superior hightemperature performance, chemical resistance, and mechanical toughness. Silicon-based microelectronic sensors that utilize a Schottky diode have been developed. This type of diode exhibits the “Schottky effect,” which results in rectifying behavior in the current of electrons leaving a metal surface when an external electric field is applied. Each sensor has a temperature detector and a heater on the same chip. The architecture of the Schottky diode makes the sensors highly sensitive to specific adsorbed gases. A picture and schematic drawing of the combined hydrogen-sensitive Schottky diode is shown in Figure 1. The detector and heater allow optimization of sensor response and recovery time. These microfabricated hydrogen sensors are highly sensitive to low concentrations of hydrogen gas. The concentration range of the combined two sensor systems-Schottky diode and resistor—is 10 ppm to 100% in nitrogen. A number of them can be placed in an area to monitor hydrogen leaks in safety applications. With hardware and software to monitor the sensors, the location and magnitude of a leak can be determined. In space transportation applications, hydrogen propellant leaks pose significant operational problems. In 1990, hydrogen leaks on the Space Shuttle while on the launch pad temporarily grounded the fleet until the source of the leak could be identified. As recently as July 1999, the launch of a Space Shuttle mission was delayed for two days due to an ambiguous signal using the present leak-detection system. Thus, the detection of explosive concentrations of fuel continues to be of interest wherever fuel is used.
MRS BULLETIN/DECEMBER 2001
Pd-alloy (PdCr or PdAg) Schottky-diode connectors
a
Pd-alloy resistor
2.2 mm
Pt heater connector
Pt temperature detector connector
Pt heater connector
b
Figure 1. (a) Schematic diagram of the silicon- based hydrogen sensor. The Pd alloy Schottky diode (rectangular regions) resides symmetrically on either side of a heater and temperature detector. The Pd alloy resistor is included for high concentration measurements. (b) Picture of the packaged sensor.
In response to this problem, efforts were made at NASA Glenn to develo
Data Loading...
