QCM SENSORS FACTS

 


QCM is an abbreviation of Quartz Crystal Microbalance.

The word Microbalance seeks to associate the Crystals ability to detect mass figuratively (here a beam scale).

The use of Quartz Crystals to detect small mass changes started to grow in the beginning of the 60’ies after G. Sauerbrey 1 showed that there is a direct correlation between a small added mass,  uniformly distributed on one or both of the electrodes deposited on the

major surfaces of a quartz crystal and a small frequency change , according to equation   where fq is the frequency and mq is the mass of the Quartz Crystal.

In order to utilize this phenomenon the Quartz Crystals normal enclosure in gas or vacuum is removed so that one or both of its surfaces can be exposed to the gas or liquid to detect minute amounts of atoms or molecules in order to study different reaction kinetics.
Shortly after the discovery of the QCM principle one major application in gas phase turned into rapid growth and became a large commercial success. Thin film monitors solved the problem to accurately and cheaply control the thin film deposition process used in vacuum equipment.

Linear and accurate mass loads up to a few % could be achieved. However over the years various methods to increase the mass load took place. Finally Lu and Lewis 2,3 extended the usable mass load range dramatically by considering the sensor as a composite resonator consisting of layers with different acoustic impedance depending on the elastic properties of the material deposited.
Glasford and Kanazawa showed that the QCM could be used in liquid applications by taking into account the viscoelastic properties of the liquid. The shear wave for a typical 5 MHz crystal used in liquid will penetrate approximately ¼ um into the liquid which is enough for making measurements and a new era opened up.
The research field of QCM has exploded during the last 20 years which can be verified by the number of scientific papers published. The application areas has at the same time moved to more advanced studies of surface interactions. Electrochemistry and Biosensors are examples of such applications.

However despite the large number of scientific papers published very few industrial applications has evolved into commercial systems beside thin film monitors. There are many explanations for this but one major reason is that although it is possible to obtain very high mass sensitivity < 1 nanogram    or less the repeatability is not always as good because many other factors contribute to change the frequency hence making the interpretation difficult. We have to conclude that many fundamental issues has been neglected and are yet to be addressed. Examples are mechanical stress in the electrodes or deposited layers or mounting, effective area (not same as electrode area), frequency vs temperature behavior, compressional waves generation, mode shape by using different blank design (plano-plano or plano-convex), vibrating mode (fundamental or overtone), drive level, shunt capacitance cancellation or not just to name a few.
Comparing with the results that are achieved in high performance OCXOs there are much more performance improvements that can be expected.

Due to our long experience in quartz crystal and oscillator design and production we have over the years learned about all these hurdles and thus can support your special needs as a very qualified partner for special requirements. Although we provide a comprehensive list of standard sensors available for QCM measurements we can customize or optimize any sensors according to your requirements or application whether it is in the gas / vacuum or liquid phase. We have supplied a vast number of QCM sensors with World Class Quality over a period of 20 years to many world leading companies. 


 

References

1. G. Sauerbrey (1959). "Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung".
    Z. Phys. 155 (2): 206-222

2. C.S. Lu and O. Lewis (1972). "Investigation of film-thickness determination by oscillating quartz resonators with large mass load".
    J. Appl. Phys. 43 (11): 4385.

3. C. Lu, A. W. Czanderna, ed. (1984). Applications of Piezoelectric Quartz Crystal Microbalances. Amsterdam: Elsevier

4. Glassford, A. P. M. J. Vac. Sci. Technol. 1978, 15, 1836. Kanazawa, K. K.; Gordon II, J. Anal. Chem. 1985, 57, 1770. Kanazawa, K. K.;
    Gordon II, J. Analytica Chimica Acta 1985, 175, 99-105.


5. C.E. Reed, K.K. Kanazawa and J.H. Kaufmann (1990). "Physical description of a viscoelastically loaded AT-cut quartz resonator".
    J. Appl. Phys. 68 (5): 1993.


6. K.K. Kanazawa and J.G. Gordon II (1985). Anal. Chim. Acta 99: 175.


 

 

Currency

Join us

Do you want to become our

Distributor,

Sales Representative or

Sales Ambassador ? 


After releasing our new website we are getting more inquiries. We realize our products are gaining interest in the market and are therefore looking to expand our sales.

If you think you have the right combination of background, interest, connections, motivation etc. and want to work with us take this opportunity and send your application with your resume either to sales@quartzpro.com or fill in a form under contact info. We will get back with more information.