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.
A Simple Method of using the Die of an Integrated Circuit to Measure the Relative Humidity Inside its Encapsulation
A technique (the capacitance-ratio test) is described for assessing the water content of hermetic packages containing an integrated circuit die. It is based on a theoretical analysis which shows that the frequency dependence of the capacitance between a selected pair of IC metallisation tracks can be used to derive the moisture induced component of this capacitance. A measurement on an encapsulated integrated circuit die, held at a constant temperature, is used to determine the ratio of the moisture induced capacitance and the intrinsic capacitance between metallisation tracks. By comparing this ratio with that obtained from a sample of integrated circuits exposed to a known relative humidity, the test can indicate whether the relative humidity in the package is greater or less than a specified value. The accuracy of the test is comparable with that of other moisture sensing methods for encapsulations, and its sensitivity is adequate for the control of known moisture-related failure mechanisms in integrated circuits.
Humidity-sensitive electrical properties and switching characteristics of BN films
Abstract This paper reports on the electrical properties of polycrystalline boron nitride (BN) films deposited on silicon substrates in a B 2 H 6 NH 3 H 2 system. Virgin (unformed) samples exhibit humidity-sensitive electrical resistances. A current obeying Ohm's law at low humidities and low fields becomes space-charge-limited at high humidities and high fields. Some of the properties fundamental to their use as humidity sensors are also examined. After electroforming, BN films in the form of Ag/BN/Si/Al sandwiches begin to exhibit threshold switching only in atmospheres containing moisture. This switching behavior depends not only on the humidity but also on the sweep speed, the frequency of oscillation and the polarity of the applied sawtooth voltage pulse trains. A revised form Dearnaley's filamentary model is proposed.