A TEMPERATURE INSENSITIVE QUARTZ MICROBALANCE

Mass deposition onto a microbalance is generally accompanied by a temp erature change. By measuring a single frequency only, it is not possib le to separate the frequency change due to mass change from that due t o temperature change. In the temperature insensitive microbalance tech nique, measurements of two frequencies, the fundamental mode and third overtone frequencies of an SC-cut resonator, yield two equations with two unknowns. This allows the separation of mass change effects from temperature change effects. Dual mode excitation can be used for highl y accurate resonator self-temperature sensing over wide temperature ra nges. SC-cut resonators are also thermal transient compensated. These unique properties allowed the development of a temperature compensated microbalance that is highly sensitive to mass changes, which can be u sed in rapidly changing thermal environments, over wide temperature ra nges, and which requires neither temperature control nor a thermometer other than the resonator. To demonstrate the performance of this micr obalance, SC-cut resonators were coated with thin polymethylmethacryla te (PMMA) photoresist films then placed into a UV-ozone cleaning chamb er that initially was at about 20 degrees C. When the UV lamp was turn ed on, the UV-ozone removed PMMA from the surfaces while the chamber t emperature rose to about 60 degrees C. The frequency changes due to ma ss changes could be accurately determined, independently of the freque ncy changes due to temperature changes.