Thin film ppb oxygen sensor

Abstract

An oxygen sensor has a sensor body formed of a crystalline material, such as zirconia, with first and second electrodes disposed on a single surface thereof. The electrodes are arranged to induce superionic oxygen transport in the body along current paths extending at a shallow depth in the crystalline material at the electrode surface. The electrodes may be interdigitated or juxtaposed porous electrodes that define an exposed surface pattern of ionic conduction for sensing, and the electrodes are preferably poisoned to inhibit cross sensitivity to reactive components, such as hydrogen, that may be present in the environment. The electrodes may effect electrode-limited superionic conduction in a thin slice of single crystal material, or a polycrystalline yttria-stabilized zirconia film sensing body, and operate at a relatively low temperature in the range of 250-400° C., preferably about 300-350° C., with negligible leakage current or cross sensitivity, allowing reliable measurement of oxygen concentrations in the ppb range. The oxygen sensor may be fabricated together with a heater, such as a resistive heating element, deposited on the back face of the sensor body, or the sensor body may be attached to a heater chip. One such heater chip includes both a heating electrode, and a resistive thermal device that may, for example, provide a feedback or control signal for controlling heater temperature in the desired range. The sensors may be lithographically formed in arrays with suitable lead pads, then scored and separated, and mounted on heater chips, providing a self-contained integrated unit of versatile application.