Patent DE-102008002157-A1 (DE)
Title: Sensor element to spectroscopically measure infrared radiation, comprises substrate, membrane formed on substrate upper side, cavity formed below the membrane in the substrate, thermopile structure, filtering device, and thermopile cells
Inventor: ULBRICH NICOLAUS
IPC: G01J3/00
Filed: 2008-06-02
Abstract: The sensor element comprises a substrate (1), a membrane formed on an upper side of the substrate, a cavity formed below the membrane in the substrate, a thermopile structure with lateral thermopile pairs, which have a first thermal shank made of a first semiconductor material and a second thermal shank made of a second semiconductor material, a filtering device provided for wavelength selective transmission of the infrared radiation over an adhesive layer on the membrane, and thermopile cells. Seebeck coefficients of the semiconductor materials are different. The sensor element comprises a substrate (1), a membrane formed on an upper side of the substrate, a cavity formed below the membrane in the substrate, a thermopile structure with lateral thermopile pairs, which have a first thermal shank made of a first semiconductor material and a second thermal shank made of a second semiconductor material, a filtering device provided for wavelength selective transmission of the infrared radiation over an adhesive layer on the membrane, and thermopile cells. Seebeck coefficients of the semiconductor materials are different. The first and second semiconductor materials have dopings of the same type of charge carrier (p, n). The first and second thermal shanks are directly contacted with one another in a contact surface. Both of the thermal shanks are p-doped or n-doped. A first insulating intermediate layer (2) covers the substrate outside of the cavity and extends itself over the cavity. A second insulating intermediate layer (4) is formed on a first semiconductor layer (3) of the first thermal shank, and a second semiconductor layer of the second thermal shank is formed on the second insulating intermediate layer. A contact opening (5), in which the contact surface is formed between the thermal shanks, is formed in the second insulating intermediate layer. The first thermal shank is structured in the first semiconductor layer. The second insulating intermediate layer covers the first insulating intermediate layer and the structured first semiconductor layer. The second semiconductor layer, in which the second thermal shank is formed, is applied on the second insulating intermediate layer. The second thermal shank is contacted with the first thermal shank over the contact surface formed in the contact opening. A third insulating intermediate layer covers the second semiconductor layer. An absorber layer is applied and structured on the third insulating intermediate layer for absorbing the incident infrared radiation. A structured metal layer is applied for contacting the first and/or the second semiconductor layers. The lateral thermopile pairs are arranged next to each other or on the membrane, where each thermopile pair is formed from the first thermal shank and the second thermal shank over the first thermal shank and contacted with the first thermal shank. The thermopile pairs are separated by trenches, which are formed in the membrane and subsequently filled with a closing layer. Access holes are formed in some trenches for etching the cavity below the membrane. A cap substrate is fastened in vacuum-tight connections on the coated and the structured substrate. A further cavity is formed in the cap substrate, so that the membrane is arranged between the cavity of the cap substrate and the cavity formed in the substrate. One of the semiconductor materials is lowly doped and the other semiconductor material is highly doped. The combination of the both semiconductor materials of the both semiconductor layers is obtained from n-silicon and n +>-silicon, p-silicon and p +>-silicon, n-germanium and n +>-germanium and n-silicon and n +>-silicon-germanium. Each of the thermopile cells has the cavity formed in the substrate and the membrane formed above the cavity with thermopile pairs. The thermopile cells are laterally formed next to each other and are mutually contacted. An independent claim is included for a method for producing a sensor element.