Microfabricated thermionic detector
View Patent ↗A microfabricated TID comprises a microhotplate and a thermionic source disposed on the microhotplate. The microfabricated TID can provide high sensitivity and selectivity to nitrogen- and phosphorous-containing compounds and other compounds containing electronegative function groups. The microfabricated TID can be microfabricated with semiconductor-based materials. The microfabricated TID can be combined with a microfabricated separation column and used in microanalytical system for the rapid on-site detection of pesticides, chemical warfare agents, explosives, pharmaceuticals, and other organic compounds that contain nitrogen or phosphorus.
1. A microfabricated thermionic detector, comprising:
a microhotplate comprising
a substrate having a suspended membrane formed thereon,
a resistive heating element disposed on a surface of the suspended membrane, and
a low work function material disposed on a surface of the suspended membrane exposed to a detection chamber to provide a thermionic source that generates negative ions from a sample gas comprising an electronegative function group;
at least one gas inlet attached to the detection chamber for introduction of the sample gas thereinto;
an exhaust gas outlet attached to the detection chamber for removal of decomposition products therefrom; and
an ion collection electrode disposed in the detection chamber proximate the thermionic source, wherein the electrode is positively biased relative to the thermionic source and collects the negative ions generated by the sample gas reacting with the thermionic source when the suspended membrane is heated by the resistive heating element and a voltage is applied between the thermionic source and the electrode.
2. The microfabricated thermionic detector of claim 1 , wherein the microhotplate is fabricated from materials selected from the group consisting of semiconductors and dielectrics.
3. The microfabricated thermionic detector of claim 2 , wherein the materials comprise silicon-based materials.
4. The microfabricated thermionic detector of claim 3 , wherein the silicon-based materials comprises materials selected from the group consisting of silicon nitride, polycrystalline silicon, silicon oxide, silicon oxynitride, and silicon carbide.
5. The microfabricated thermionic detector of claim 1 , wherein the resistive heating element comprises a metal selected from the group consisting of platinum, molybdenum, titanium, chromium, palladium, gold, tungsten, and combinations thereof.
6. The microfabricated thermionic detector of claim 1 , wherein the detection chamber comprises a lid and wherein the ion collection electrode is disposed on the lid.
7. The microfabricated thermionic detector of claim 1 , wherein the ion collection electrode is disposed on the substrate.
8. The microfabricated thermionic detector of claim 1 , wherein the low work function material comprises an alkali-containing material.
9. The microfabricated thermionic detector of claim 8 , wherein the alkali-containing material comprises cesium or rubidium.
10. The microfabricated thermionic detector of claim 1 , wherein the low work function material comprises a sol gel.
11. The microfabricated thermionic detector of claim 1 , wherein the low work function material comprises an alkaline-earth-containing material.
12. The microfabricated thermionic detector of claim 11 , wherein the alkaline-earth-containing material comprises strontium.
13. The microfabricated thermionic detector of claim 1 , wherein the low work function material comprises TiN or LaB 6 .
14. The microfabricated thermionic detector of claim 1 , wherein the sample gas comprises a nitrogen- or phosphorous-containing compound.
15. The microfabricated thermionic detector of claim 1 , wherein the sample gas comprises a halogen-containing compound.
16. The microfabricated thermionic detector of claim 1 , wherein the detection chamber has a cross-sectional dimension of less than three millimeters.
17. The microfabricated thermionic detector of claim 1 , wherein the detection chamber has a height of less than one millimeter.