Quartz Crystal Microbalance Surface Flatness & Finish

The Quartz Crystal Microbalance (QCM) is a key component used in a variety of research and industrial instruments to detect and monitor the small variation of mass, adsorption, density and corrosion, etc. As an extremely sensitive mass sensor capable of measuring mass change in the nanogram range, the manufacturing of QCM requires stringent quality control to ensure its precision. Any surface defect on the QCM plate may cause significant measurement inaccuracy and errors.

Reliable quality control heavily relies upon accurate, quantifiable and reproducible surface inspection. Flatness and finish of the QCM surface are vital to its accuracy and both measurements in 3D guarantee proper manufacture processing and control measures. Unlike a touch probe technique, the NANOVEA Profilometer performs a 3D non-contact surface measurement of the sample. This eliminates the risk of creating micro scratches on the QCM surface that may cause inaccuracy or errors in the mass measurement.

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An array of 3 × 3 images is automatically taken and stitched by the NANOVEA ST400, as shown in Fig. 2, for a larger microscopic observation of the QCM sample. The area of interest is then chosen for 3D scan.

The false color view and the 3D view of the QCM sample surface are shown in Fig. 3, allowing users to observe the QCM sample from different angles and magnifications. Flatness variation can be seen clearly by color and height changes at the top of the QCM sample. The center of the QCM sample is slightly elevated compared to the edge. The flatness is 246 µm according to the ISO 12781 standard, as calculated by the NANOVEA analysis software. The QCM is an extremely sensitive and accurate device capable of detecting mass change down to 0.1 nanogram. The flatness and uniformity of the QCM play an important role in ensuring its quality and accuracy.

The 3D non-contact surface scan provides a useful tool to determine the surface finish quality with high precision. Fig. 4 shows the QCM sample surface after form removal. The finish values are calculated and summarized in Table 1. Fig. 5 presents the surface morphology of the QCM sample at a high magnification. Depending on the applications of the QCM, such as monitoring thin film deposition and cell growth, the QCM requires different surface finishes. The capacity of high resolution scan enables users to measure the detailed morphology and tiny surface features. Moreover, it can pick up any undesired defects including scratches or cracks on the sample surface.

Fig. 6 displays the light intensity map of the QCM sample surface. The metal electrode shows a much higher intensity compared to the quartz substrate. This function provides users additional information that may be used to determine the different materials or phases on the sample surface.

In this application, we have showcased that the NANOVEA ST400 3D Non-Contact Profilometer performs surface inspection on a QCM sample with high accuracy. The automatic microscope image array enables observation of a larger surface under the microscope. The 3D non-contact surface scan is a very useful quality control tool to determine whether the manufactured QCMs fall in line with specifications including finish and flatness.

The data shown here represents only a portion of the calculations available in the analysis software. NANOVEA Profilometers measure virtually any surface in fields including Semiconductor, Microelectronics, Solar, Fiber Optics, Automotive, Aerospace, Metallurgy, Machining, Coatings, Pharmaceutical, Biomedical, Environmental and many others.