## Materials and Methods
### OPS and LTM Experimental Setups  
The Device Under Test (DUT) consists of a microgripper prototype made up of pseudo-rigid beams and flexure hinges. Any jaw of the microgripper is actuated by a capacitive rotary comb-drive that provides a torque when a voltage is applied to the electrodes. During the first experimental campaign, performed with the Optical Profiling System, a variable voltage source has been used to supply the DUT and to evaluate the angular displacements of its comb drive. In this investigation, a power supply Keithley 236 SMU with 0.06 V output voltage accuracy (Range \(\pm\)110.00 V) has been used (Figure 2). \begin{table}
\begin{tabular}{l l} \hline
**Device** & **Characteristics** \\ \hline \multirow{2}{*}{DUT Material} & Silicon type P, dopant Boron, orientation \textless{}100\textgreater{}, electrical \\  & resistivity 0.005–0.030 Ohm\textless{}cm \\ \hline \multirow{2}{*}{DUT Geometry} & module dimensions 2000 \(\upmu\)m \(\times\)1500 \(\upmu\)m, device thickness 40 \(\upmu\)m, insulated layer thickness 3 \(\upmu\)m, handle thickness 400 \(\upmu\)m \\ \hline \multirow{2}{*}{Power Supply} & Keithley 236, Range settable to 1.1/11/110/1100 V with \\  & respectively 0.1/1/10/100 mV resolution, accuracy 0.06 V \\  & (Range \(\pm\)110.00 V) \\ \hline \multirow{2}{*}{Micropositioner} & n.1 MP25L, n.1 MP25R, range X/Y/Z 10/10/10 mm with \\  & 5 \(\upmu\)m resolution \\ \hline Probes (supply) & PA-C-1M with tungsten needles \\ \hline \multirow{2}{*}{DUT Stage} & The wafer containing the DUT is placed on the profilometer \\  & working surface and fixed by an adhesive tape \\ \hline \multirow{2}{*}{3D Optical Profilometer} & Fogale Zoomsurf 3D optical profiling system, field of view from \\  & 7.2 mm \(\times\) 5.4 mm to 80 nm \(\times\) 60 nm, maximum lateral \\  & resolution 0.6 \(\upmu\)m \\ \hline Digital Image & 768 \(\times\) 580 pixels, 8 bit, 0.6 px/\(\upmu\)m \\ \hline Image Processing Software & In-house software developed in MATLAB (2017a, MathWorks) \\ \hline Notebook pc & Intel core i7-2670, 6 Gb RAM, Nvidia GeForce GT 520 MX \\ \hline \end{tabular}
\end{table} 
Table 1: Optical Profilometer System (OPS) experimental setup: specifications of the comb-drive actuated silicon microgripper (Device Under Test, DUT) and of the testing stand. \begin{table}
\begin{tabular}{l l} \hline
**Device** & **Characteristics** \\ \hline \multirow{2}{*}{Power Supply} & HP E3631A, DC Output: 0 to +25 V, 0 to \(-\)25 V, Resolution \\  & 1.5 mV, Accuracy 0.04 V at F.S. \\ \hline \multirow{2}{*}{DUT Stage} & Instrumented support with micrometric screws for angular and \\  & linear movement of the sample, in the 3 orthogonal directions in \\  & space (x, y, z) \\ \hline \multirow{2}{*}{Light microscope} & Eurotek NB50 TS NB SOTS, Zoom range 0.8\(\times\)...5\(\times\) (8\(\times\)...50\(\times\)), \\  & LED illumination Transmitted-Reflected, B2-1525 additional \\  & objective 2\(\times\) \\ \hline Digital Image & 1920 \(\times\) 1080 pixels, 24 bit, 1.359 px/\(\upmu\)m \\ \hline Digital camera & MD6 iS, 6 MP, pixel dimension, 2.8 \(\upmu\)m \(\times\) 2.8 \(\upmu\)m, maximum \\  & resolution 3264 \(\times\) 1840 px \\ \hline \multirow{2}{*}{Image Processing Software} & In-house software developed in MATLAB environment (2017a, MathWorks) \\  & (2017a, MathWorks) \\ \hline \end{tabular}
\end{table} 
Table 2: Light Trinocular Microscope (LTM) experimental setup (DUT, micropositioner, probes and PC as in Table 1). Two micropositioners with 5 \(\upmu\)m resolution have been used, each one being equipped with tungsten needles, in order to apply the voltage to the DUT electrodes, Figure 3, and a set of digital images have been acquired using a Fogale Zoomsurf 3D OPS. The digital image resolution of 0.6 pixel/\(\upmu\)m is provided by the Profilometer embedded software. During the image acquisition campaign performed by means of the LTM system the same microgripper sample has been analyzed. The power supply device is a HP E3631A, with 0.04 V output voltage accuracy (Range 0 to +25 V).