Slot-die coating is a method of coating a wide layer of thin film on a substrate. It has the advantages of large-area coating with high reproducibility and uniform thickness. For this reason, it has been widely applied in various industrial manufacturing fields. To secure higher coating uniformity under various coating conditions, estimating and controlling the flow rate of the coating solution discharged to the substrate is crucial. In this study, a practical gravimetric flow rate measurement method for slot-die coating uniformity evaluation has been introduced. The gravimetric method is a technique for accurately and quickly estimating the flow rate through the mass change over time using a precision weighing balance. We analyzed the measurement principle and errors caused by fluid mechanics such as hydrodynamic force or capillary force. The dynamic properties based on fluid viscosity were also evaluated for flow rates from 5 to 50 μL/s. The repeatability of the fabricated measurement system was ~1.5 μL/s. Finally, it was confirmed that the settling time for high-viscosity fluid could be advanced by 56.4% through multi-step feedforward control.

The electromagnetic force compensation (EMFC) measurement principle has been widely adopted in the high-precision mass metrology system due to its sensitive compliant mechanism and nanometer level position sensor. In EMFC, an electromagnetic actuator balances the gravitational weight to maintain zero (or Null) position by feedback control using a position sensor, and the weight is calculated from the current applied to the actuator. Thus, a position sensor in the EMFC system should measure the null position accurately with high sensitivity and resolution. The position sensor commonly used in EMFC balance is an optical sensor that measures the displacement of EMFC balance from the intensity of light coming through a slit using a two-segment photodiode. This paper analyzed the characteristics of an optical position sensor for EMFC balance through parametric analysis using the Fresnel diffraction model. We also evaluated the performance of the sensor and confirmed the feasibility from weighing performance of the balance prototype. Normalized sensitivity of the sensor was 0.04237 μm^-1 and measured resolution was 1.09 nm. The weighing repeatability with our optical position sensor was 4.83 mg (1σ) at 10 g measurement, which was 3 times better than the repeatability with an alternative commercial sensor.