Development and Characterization of an Electroplated Copper Nickel Alloy–Platinum Micro-Thermocouple

A cost effective electrodeposition technique was developed to microfabricate copper nickel alloy (CuNi)-platinum micro thermocouples. A flat smooth silicon wafer with a 9000 Å layer of oxide was chosen as the substrate material. Gold was used for the thermocouple electroplating base because of its high resistance to electrochemical corrosion and oxidation. Since gold does not adhere to the silicon substrate, a chromium layer was deposited as a seed layer for the gold deposition. The substrate is patterned using a lithography process to create a mould for the plating with junction sizes in the range 50 μm to 500 μm. The CuNi leg was electroplated onto the exposed gold surface. The platinum leg of the thermocouple was metal deposited. The CuNi composition of the microfabricated thermocouples was 16.3 percent nickel and 83.7 percent copper as determined through energy dispersive spectroscopy. The sensitivity of the microthermocouple was determined using a thermal bath, with the platinum leg as a reference. The sensitivity was 39 μV/°C for ice bath compensated and 41 μV/°C for non compensated thermocouples.