Indium Tin Oxide Non-Magnetic Heating Film for Miniaturized SERF Gradient Magnetometer

Abstract

We propose non-magnetic heating film based on indium tin oxide (ITO) and apply it in a miniaturized spin exchange relaxation free (SERF) gradient magnetometer. To achieve ultrahigh sensitivity, alkali metal atoms inside the vapor cell of the magnetometer require an elevated temperature field that is stable and uniform. ITO is a transparent and electrically conductive material which is suitable for such application and can be used as resistance wire to form the heating film. A film structure composed of an insulation layer sandwiched between two ITO layers with the same optimized pattern is used to configure the heating current to double back on itself to reduce the magnetic noise caused by it. Experiments show the proposed film can be heated to over 200 °C, which is sufficient for vaporizing alkali metal atoms such as potassium, rubidium, and cesium. The magnetic current coefficients of the heating films are below 0.2 nT/mA and with the high frequency heating current, low-frequency magnetic noise can be further reduced. We compare ITO-based heating films and conventional flexible printed circuit (FPC) heating films side by side in the same gradient magnetometer and with ITO films a more uniform temperature field and better intrinsic magnetic field sensitivity of 22 fT/cm/Hz $^{1/2}$ is achieved. The proposed ITO-based non-magnetic heating film can be used not only in atomic magnetometers but also in other atomic devices such as chip scale gyroscopes and atomic clocks.