[t-Nova Series - Applications]
The area of glass substrates for large displays is increasing while their thickness is decreasing, which raises the importance of thickness measurement. Because the thickness of the glass substrate determines the overall thickness of the display device, it must be controlled. If the thickness is nonuniform, unwanted refractive effects may occur, distorting the displayed image or even causing physical damage to pixels. Therefore, precise measurement of glass substrate thickness is required to improve yield in large-format display production.
Meter-Lab’s t-Nova series is based on a non-contact optical measurement method and uses spectral-domain interferometry among optical techniques, enabling sensors that measure samples with high resolution down to 10 nm, making them well suited for precise glass-substrate thickness measurement. Among them, the t-Nova-1550R — a reflective, high-precision optical thickness sensor — illuminates a sample with light centered at 1550 nm and detects the reflected light to measure thickness (assuming refractive index n = 1.5) from 2 μm to 3 mm.
Figure 1. (a) Glass of thickness 1.09 mm and (b) glass of thickness 2.15 mm
Figure 1 shows the optical windows (BK7) of the glass samples used for measurement (50 mm diameter). The thicknesses measured by placing the vernier caliper on the top and bottom surfaces of each sample were 1.09 mm and 2.15 mm, respectively.
Figure 2. Experimental setup for glass thickness measurement using t-Nova-1550R
Figure 2 shows the experimental setup for measuring glass thickness with the t-Nova-1550R. We used a compact, lightweight probe (30 mm diameter, 60 mm length) for a simple configuration. The probe can measure at a distance of several tens of millimeters without contacting the sample. The instrument on the left is Meter-Lab’s s-Nova-1550, a domestically developed near-infrared spectrometer. The t-Nova-1550R incorporates our spectrometer and has been optimized for performance.
Figure 3. Interference spectra and thickness values measured with t-Nova-1550R
Figure 3 presents the measurement results for each sample obtained with the t-Nova-1550R. Thickness values are calculated from the interference spectra acquired for each sample. The thicknesses measured by the t-Nova-1550R were 1.09166 mm and 2.14519 mm, respectively. These results agree with the vernier caliper measurements (1.09 mm and 2.15 mm) and confirm the capability of measurement with high resolution on the order of 10 nm.
With its non-contact optical, high-precision thickness measurement performance, Meter-Lab’s t-Nova-1550R is expected to be widely applicable in various display manufacturing processes.
