The Moisture Dependence of the Electrical Sheet Resistance of Aluminum Oxide Thin Films with Application to Integrated Moisture Sensors
The measurement of moisture inside integrated circuit packages for reliability purposes involves either destructive mass spectroscopic tests, measurement of the impedance between interdigitated electrode pairs, or measurement of the capacitance of a parallel plate capacitor with a porous upper electrode and a dielectric of anodized aluminum oxide. This paper reports the use of an integrated circuit that combines interdigitated electrodes with a pair of matched field-effect transistors to permit sensitive, quantitative measurement of the moisture dependence of the sheet resistance of very thin filmis of oxidized aluminum. Data analysis is based on an equivalent circuit model for the device. It is found that the room temlperature sheet resistance of a 1500 Å film varies from 2 × 1015 Ohms/sq. at an ambient dew point of ¿43°C to 2 × 1010 Ohms/sq. at a dew point of +22°C. The device retains useful sensitivity below dew points of ¿60°C, and because of the absence of a porous upper electrode, exh ibits rapid response to changes in ambient moisture. Fabrication details, reproducibility, hysteresis, and aging of these devices is discussed.
Solid-state humidity sensors
Abstract The applicability of semiconductor technology to the realization of general-purpose humidity sensors is discussed. Examples of solid-state dew-point sensors are given. Special attention is paid to the construction and properties of integrated capacitive dew-point sensors.
A Capacitance Humidity-Sensing Transducer
Recent improvements in the design of humidity-sensing transducers and the materials used in their construction have minimized many of the past limitations. A new capacitance humidity sensor is described that has a design, construction, and material composition that impart a unique combination of properties. This humidity sensor also has an ease of fabrication that makes it an improvement over other capacitance-type humidity sensors. The humidity-sensitive film is a multilayered polymeric film consisting of a humidity-sensitive dielectric core, two conductive layers, and two bottom layer strips. The element has a nominal capacitance of 1000 pF and a humidity sensitivity of approximately 4.0 pF/percent RH at 50-percent RH. The characteristics of the humidity sensor, which include the element's sensitivity to relative humidity, response characteristics, and the effects of temperature, are discussed.