What is QCM?

Basic Principles and NDK's High-Precision Sensor Technology

QCM is a technology capable of highly sensitive detection of mass changes in the nanogram range, and is applied to various surface evaluations and gas monitoring. This page introduces its principles and applications.

QCM Principle

QCM is a measurement technology that uses a quartz crystal oscillator to detect minute mass changes with high sensitivity. The quartz crystal oscillator has the characteristic of oscillating stably at a constant frequency. When a substance adheres to its surface, the resonant frequency decreases proportionally to the amount of material deposited (this is called the mass loading effect). Based on this frequency change, it is possible to capture minute mass changes at the nanogram level in real time.

※This relationship between mass and frequency is quantified by Sauerbrey's equation, which boasts high reproducibility and reliability.

A relational expression between mass and frequency

Sauerbrey equation for the relation between masses and frequencies has been known.

【Sauerbrey's equation】
Sauerbrey's equation is often used as a function of mass/frequency in applications such as uniform and rigid thin films.
For example, when calculating a certain mass amount and thin film thickness in vacuum deposition., the equation is used.
According to sauerbrey equation, the mass-equivalent per Hz frequency variation is about 4.18 ng per cm2 with 10MHz crystal sensor.

Features of NDK's Proprietary Twin-QCM^® Structure

What is Twin-QCM^® ?

Twin-QCM^® is NDK's proprietary high-precision QCM sensor that integrates both a detection electrode and a reference electrode onto a single quartz crystal.
By measuring the frequency difference between the two electrodes, external disturbances such as temperature, vibration, and stress are effectively canceled out, enabling stable detection of mass changes.

Feature 1: Significantly Cancels External Disturbances

While the frequency of a quartz crystal changes due to temperature variations and mechanical stress, the Twin-QCM^® sensor effectively eliminates the influence of these external factors by measuring the frequency difference between the detection electrode and the reference electrode.

Feature 2: Built-in Temperature Sensor

Accurately monitors and controls electrode temperature to achieve even higher measurement precision.

Frequency Temperature Characteristics (Reference Values):

Temperature Range: -70°C to +125°C
Frequency Change per Electrode: Approx. ±100 ppm (at 25°C)
Differential Frequency Change: Within ±10 ppm (*After Temperature Compensation)

【 Twin-QCM^® Sensor Frequency Temperature Characteristics 】

Compared to conventional QCM sensors, Twin-QCM^® reduces temperature induced errors to less than one-tenth, providing high stability and reproducibility.

Thermogravimetric Analysis Using QCM (QTGA Method)

What is the QTGA Method (QCM Thermogravimetric Analysis)?

The QTGA method is an analytical technique that incorporates temperature control into QCM to observe mass changes in real time during heating and cooling.
Unlike conventional TGA (Thermogravimetric Analysis), it can be used in vacuum, low-pressure, and cryogenic environments, excelling in detailed analysis of desorption and adsorption behavior.