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.
Moisture sensing in transformer oil using thin-film microdielectrometry
In-situ moisture sensing in transformer oil by measuring the change in dielectric properties of 1- to 7- mu m-thick layers of plasma-deposited bromobenzene coated on interdigitated 50- mu m-wavelength electrodes of a microdielectrometer chip is demonstrated. Gain-phase measurements in the frequency range of 0.0005 to 10000 Hz, normalized to the frequency of peak phase shift, are found to be universal. Evidence is presented that the coatings act as semipermeable membranes serving as barriers to the transformer oil, but absorbing moisture in proportion to its absolute content in the oil. Sensitivity to moisture from less than 5 to about 50 p.p.m. is found with a transient response of less than a few minutes. Although the method is well suited to following the dynamics of water in paper-oil systems over periods of days or perhaps weeks, a long-term loss of sensitivity must be overcome if the sensor is to be used without recalibration for extended periods of time. Its use for discerning abnormal behavior in a pilot transformer monitoring system is described. >
Photoinduced spin-state transition of Co3+ in the layered perovskite manganite thin film
The photoinduced effect, at different temperatures, on layered perovskite manganite La1.2Sr1.8Mn1.8Co0.2O7 thin film deposited on a SrTiO3(100) substrate has been studied using a He–Ne laser (632.8 nm) with the power of output 25 mW at low temperatures. The electrical transport and magnetic properties of the film are investigated systematically in the temperature region from 20 to 300 K. The resistance shows a significant decrease at low temperatures (T<90 K) under laser irradiation, which can be interpreted in terms of the spin-state transition of Co3+ ions. The magnetic field combined with the laser is also used to detect the photoinduced effect of the spin-glass state. The time dependence of the metastable system under several applied fields was also discussed. The system has the ability to keep a persistent memory of the magnetic history imprinted in its zero-field resistance.