P-n junction based thermal detector

Abstract

A thermopile-based thermal detector is provided by a thermocouple, formed from a single sheet of material, which is made dissimilar with a P-doped and an N-doped junction electrically isolated via a naturally forming depletion region. The thermopile P-N sheet is uniform and planar, addressing stress and manufacturing issues. The usual non-active area of a conventional thermopile is significantly reduced or eliminated, and thus the output signal per unit diaphragm area of the detector is substantially increased, without the typical reduction in the signal-to-noise ratio. Also, a significant reduction in size of the thermal detector area is provided without a reduction in signal or signal-to-noise ratio. In an aspect, a second layer of thermocouples is axially positioned over, and connected with, a first layer of thermocouples. Additional axially stacked thermopiles can be provided within the same fabrication process. Signal processing circuitry may be electrically interconnected with the thermocouple.

1 . A thermal detector comprising:
 a substrate defining a cavity;   a diaphragm having a first portion positioned over the cavity for receiving thermal energy, and a second portion at a perimeter of the diaphragm supported by the substrate;   a first layer of at least one material pair formed on a first sheet of material extending in between the diaphragm and the substrate;   a second layer of the at least one material pair formed on a second sheet of material extending in between the diaphragm and the substrate and being axially positioned over the first layer, an electrically insulating material being positioned in between the first layer and the second layer whereby the at least one material pair on the first layer is electrically isolated from the at least one material pair on the second layer, said at least one material pair on the first and second layer including a first and second leg having dissimilar electrically conductive materials, and the dissimilar materials include the first leg being a P-doped junction and the second leg being an N-doped junction, and the first leg and the second leg are electrically isolated via a depletion region; and   at least one thermocouple being configured generally perpendicular to the first and second sheet of material, said at least one thermocouple being formed between a leg of the at least one material pair on the first layer in electrical connection to a leg of the at least one material pair on the second layer, and the leg of the at least one material pair on the first layer and the leg of the at least one material pair on the second layer being dissimilar electrically conductive materials;   wherein the at least one thermocouple defines a hot junction located on the first portion of the diaphragm and a cold junction located on the second portion of the diaphragm.   
     
     
         2 . The thermal detector as in  claim 1 , wherein the at least one thermocouple material pair is created by depositing poly-silicon by chemical vapor deposition, implanting a P-type dopant, depositing a sacrificial silicon dioxide on the P-type doped polysilicon, photolithographically forming a proposed P-type dissimilar area and a proposed N-type dissimilar area, removing the sacrificial silicon dioxide by etching, and thermally depositing an N-type dopant on the proposed N-type dissimilar area. 
     
     
         3 . The thermal detector as in  claim 1 , wherein the at least one thermocouple further includes the at least one thermocouple being formed by electrical connection at the hot junction between dissimilar materials on the first and second layers, and the at least one thermocouple having electrical connection to a further thermocouple being formed at the cold junction between dissimilar materials on the first and second layers, and said further thermocouple being generally perpendicular to the first and second sheet and adjacent to the at least one thermocouple without an intermediate space in between. 
     
     
         4 . The thermal detector as in  claim 1 , wherein the diaphragm is shaped in a form of at least one of circular, rectangular, polygonal, and rectangular having rounded corners shape, and wherein the legs of the at least one thermocouple are wedge-shaped and narrower at the hot junction as compared to the cold junction. 
     
     
         5 . A method for establishing a thermal detector comprising:
 creating a substrate defining a cavity;   creating a diaphragm having a first portion positioned over the cavity for receiving thermal energy, and a second portion at a perimeter of the diaphragm supported by the substrate;   creating a first layer of at least one material pair formed on a first sheet of material extending in between the diaphragm and the substrate, and the first layer of the at least one material pair including legs having dissimilar electrically conductive materials, wherein the dissimilar materials include a P-doped and N-doped junction electrically isolated via a depletion region;   creating a second layer of at least one material pair formed on a second sheet of material extending in between the diaphragm and the substrate and being axially positioned over the first layer, and an electrically insulating material being positioned in between the first layer and the second layer whereby the at least one material pair on the first layer is electrically isolated from the at least one material pair on the second layer, and the second layer of the at least one material pair including legs having dissimilar electrically conductive materials, and the dissimilar materials include a P-doped and N-doped junction electrically isolated via a depletion region; and   creating at least one thermocouple being configured generally perpendicular to the first and second sheet of material, said at least one thermocouple being between a leg of the at least one material pair on the first layer in electrical connection to a leg of the at least one material pair on the second layer, and the leg of the at least one material pair on the first layer and the leg of the at least one material pair on the second layer being dissimilar electrically conductive materials;   wherein the at least one thermocouple defines a hot junction located on the first portion of the diaphragm and a cold junction located on the second portion of the diaphragm.   
     
     
         6 . The method as in  claim 5 , wherein the steps of creating the first layer of at least one thermocouple pair and creating the second layer of the at least one thermocouple material pair further include forming the at least one thermocouple pair on the first and second thermocouple layers by depositing poly-silicon by chemical vapor deposition, implanting a P-type dopant, depositing a sacrificial silicon dioxide on the P-type doped polysilicon, photolithographically forming a proposed P-type dissimilar area and a proposed N-type dissimilar area, removing the sacrificial silicon dioxide by etching, and thermally depositing an N-type dopant on the proposed N-type dissimilar area. 
     
     
         7 . The method as in  claim 5 , wherein the step of creating the at least one thermocouple further includes the at least one thermocouple being formed by electrical connection at the hot junction between dissimilar materials on the first and second layers, and the at least one thermocouple having electrical connection to a further thermocouple being formed at the cold junction between dissimilar materials on the first and second layers, and said further thermocouple being generally perpendicular to the first and second sheet and adjacent to the at least one thermocouple without an intermediate space in between. 
     
     
         8 . The method as in  claim 5 , wherein the step of creating the diaphragm further includes the diaphragm being shaped in a form of at least one of circular, rectangular, polygonal, and rectangular having rounded corners, and wherein the steps of creating the at least one thermocouple further includes the legs of the at least one thermocouple being wedge-shaped and narrower at the hot junction as compared to the cold junction.