**3. Experimentation Details**

The average stress through the thickness of the film is evaluated using the methods described in Section 2.1. The slope of the stress versus FN<sup>2</sup> curve, α, is determined using a linear fit to the measured stress data. The local stress of each individual layer required to compensate for the through-thickness stress gradient is calculated using Equation (3). Cantilevers with a width of 50 µm and a length of 200 µm are realized in 500 nm thick Al0.68Sc0.32N films with out-of-plane displacements measured from the difference between the anchor and beam tip heights. The Al1−xScxN cantilever fabrication is shown in Figure 1 and begins with deposition of Al0.68Sc0.32N on 100 mm p-type (100) Si wafers in an Evatec CLUSTERLINE® 200 II Physical Vapor Deposition System in steps (a) and (b). Table 1 summarizes the DC reactive co-sputtering parameters used to deposit the Al0.68Sc0.32N films. The Al1−xScxN films are deposited on a 15 nm thick AlN seed layer and a 35 nm thick gradient seed layer (Al1→0.68Sc0→0.32N) where the Sc alloying ratio is linearly varied through the thickness from 0 to 32%. This seed and gradient layer was previously demonstrated to suppress anomalously oriented grains while maintaining crystal quality [3]. The crystal quality characterized in a previous study using the full width half maximum (FWHM) of a rocking curve omega-scan showed a FWHM of 2.18◦ with the seed layer and 2.23◦ without the seed layer for films of 500 nm total (film plus seed) thickness. In step (c) Plasma Enhanced Chemical Vapor Deposition (PECVD) Silicon Nitride (SiN) is deposited and patterned using CF<sup>4</sup> reactive ion etching (RIE) to form a hard mask for Al1−xScxN etching. In step (d) aqueous Potassium Hydroxide (KOH in 45% H2O) at 45 ◦C for 100 s is used to etch the Al1−xScxN and define the cantilever dimensions with SiN protecting the Al1−xScxN film where etching is undesired. Finally, in step (e) the SiN hard mask is stripped using CF<sup>4</sup> RIE and the Al1−xScxN cantilevers are released from the substrate using isotropic XeF<sup>2</sup> dry etching. After release, the cantilever out-of-plane deflection is measured using a VHX-5000 Digital Microscope Multiscan.

**Table 1.** Summary of sputter deposition parameters for Al0.68Sc0.32N.


**Table 1.** Summary of sputter deposition parameters for Al0.68Sc0.32N.

**Process Parameter Value**  Temperature 350 °C

N2 Flow 20–30 sccm Film Thickness 100–1000 nm Base Pressure <3 × 10−7 mbar

Sputter Power Al Cathode 1000 W Sputter Power Sc Cathode 555 W DC Pulsing Frequency 150 kHz

**Figure 1.** Fabrication process for realizing Al1−xScxN cantilevers with (**a**) p-type (100) Si wafer (**b**) Al1−xScxN deposition using Evatec CLUSTERLINE® 200 II PVD system (**c**) PECVD SiN deposition and patterning using CF4 RIE (**d**) KOH in 45% H2O etch of Al1−xScxN (**e**) SiN hard mask stripped using CF4 RIE and Al1−xScxN cantilevers released using isotropic XeF2 dry etching. **Figure 1.** Fabrication process for realizing Al1−xScxN cantilevers with (**a**) p-type (100) Si wafer (**b**) Al1−xScxN deposition using Evatec CLUSTERLINE® 200 II PVD system (**c**) PECVD SiN deposition and patterning using CF<sup>4</sup> RIE (**d**) KOH in 45% H2O etch of Al1−xScxN (**e**) SiN hard mask stripped using CF<sup>4</sup> RIE and Al1−xScxN cantilevers released using isotropic XeF<sup>2</sup> dry etching.

#### **4. Results and Discussion 4. Results and Discussion**
