Temperature and humidity sensors capable of detecting temperatures and humidity are disclosed in, for example, Japanese Unexamined Utility Model Registration Application Publication No. 7-20536 (Patent Document 1), Japanese Unexamined Patent Application Publication No. 6-148122 (Patent Document 2), and Japanese Unexamined Patent Application Publication No. 58-70153 (Patent Document 3). These temperature and humidity sensors include a moisture sensitive film for humidity measurement and detect humidity based on a change in magnitude of resistance or electrostatic capacity.
Further, detection of electrostatic capacity of a humidity sensor using an oscillation circuit is disclosed in Japanese Unexamined Patent Application Publication No. 61-14556 (Patent Document 4) and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2012-508877 (Patent Document 5), for example.
Patent Document 1: Japanese Unexamined Utility Model Registration Application Publication No. 7-20536.
Patent Document 2: Japanese Unexamined Patent Application Publication No. 6-148122.
Patent Document 3: Japanese Unexamined Patent Application Publication No. 58-70153.
Patent Document 4: Japanese Unexamined Patent Application Publication No. 61-14556.
Patent Document 5: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2012-508877.
It can be considered to configure an oscillation circuit as disclosed in Patent Documents 4 and 5 using capacitance and resistance of a humidity sensor based on an electrostatic capacity technique as disclosed in Patent Documents 1 through 3 as well as inductance of an inductor that is provided separate from the humidity sensor.
In the case where an oscillation circuit is a CR oscillation circuit, because, in general, the phase rotation is gentle and oscillation frequency precision is low, and the circuit is susceptible to parasitic capacitance and resistance components, electrostatic capacity of a humidity sensor is required to be large. Accordingly, in a humidity sensor in which a moisture sensitive film is provided between two electrodes like the sensors in Patent Documents 1 and 2, areas of the electrodes need to be enlarged, thickness of the moisture sensitive film needs to be thinned, and so on. However, miniaturization of the sensor becomes difficult if the areas of the electrodes are enlarged, and an amount of change in electrostatic capacitance becomes small and the manufacturing of the sensor becomes difficult if the thickness of the moisture sensitive film is thinned. In a humidity sensor provided with linear electrodes like the sensor in Patent Document 3, intervals between the electrodes need to be narrowed. However, narrowing the intervals makes it difficult to manufacture the sensor.