Evaluation of Residual Stress of C Oriented AlN/Si (111) and Its Impact on Mushroom Shaped Piezoelectric Resonator

Aluminum nitride-based MEMS resonators are one of the interesting recent research topics for its tremendous potential in a wide variety of applications. This paper focuses on the detrimental effect of residual stress on the AlN based MEMS resonator design for acoustic applications. The residual stress in the sputtered c axis (<001>) preferred oriented AlN layers on Si (111) substrates are studied as a function of layer thickness. The films exhibited compressive residual stresses at different thickness values: -1050 MPa (700 nm), -500 MPa (900 nm), and -230 MPa (1200 nm). A mushroom-shaped AlN based piezoelectric MEMS resonator structure has been designed for the different AlN layer thicknesses. The effect of the residual stresses on the mode shapes, resonant frequencies, and quality factor (Q) of the resonator structures are studied. The resonant frequency of the structures are altered from 235 kHz, 280 kHz, and 344 kHz to 65 kHz, 75 kHz and 371 kHz due to the residual stress of -1050 MPa (thickness: 700 nm), -500 MPa (thickness: 900 nm) and -230 MPa (thickness: 1200 nm) respectively. At no residual stress, the quality factors of the resonator structures are 248, 227, 241 corresponding to the 700 nm, 900 nm, and 1200 nm thick AlN layers respectively. The presence of the residual stress reduced the Q values from 248 (thickness: 700 nm), 227 (thickness: 900 nm), 241 (thickness: 1200 nm) to 28, 53, and 261 respectively.

Preferred oriented cation configurations in high pressure phases IV and V of methylammonium lead iodide perovskite

A microscopic viewpoint of structure and dipolar configurations in hybrid organic–inorganic perovskites is crucial to understanding their stability and phase transitions. The necessity of incorporating dispersion interactions in the state-of-the-art density functional theory for the $$CH_3NH_3PbI_3$$ C H 3 N H 3 P b I 3 perovskite (MAPI) is demonstrated in this work. Some of the vdW methods were selected to evaluate the corresponding energetics properties of the cubic MAPI with various azimuthally rotated MA organic cation orientations. The highest energy barrier obtained from PBEsol reaches 18.6 meV/MA-ion, which is equivalent to 216 K, the temperature above which the MA cations randomly reorient. Energy profiles calculated by vdW incorporated functionals, on the other hand, exhibit various distinct patterns. The well-developed vdW-DF-cx functional was selected, thanks to its competence, to evaluate the total energies of different MA dipolar configurations in $$2\times 2\times 2$$ 2 × 2 × 2 cubic supercell of MAPI under pressures. The centrosymmetric arrangement of the MA cations that provide zero total dipole moment configuration results in the lowest energy state profiles under pressure, while the non-centrosymmetric scheme displays a unique behaviour. Despite being overall unpolarised, the latter calculated with PBEsol leads to a rigid shift of energy from the profile obtained from the dispersive vdW-DF-cx functional. It is noteworthy that the energy profile responsible for the maximum polarised configuration nevertheless takes the second place in total energy under pressure.

Fabrication and characteristics of highly $$\langle {110} \rangle $$-oriented nanotwinned Au films

Fine grained and nanotwinned Au has many excellent properties and is widely used in electronic devices. We have fabricated $$\langle {110} \rangle $$ ⟨ 110 ⟩ preferred-oriented Au thin films by DC plating at 5 mA/cm2. Microstructure analysis of the films show a unique fine grain structure with a twin formation. Hardness tests performed on electroplated $$\langle {110} \rangle $$ ⟨ 110 ⟩ Au films show a hardness 47% greater than random and untwinned Au. We then achieved direct bonding between two Au $$\langle {110} \rangle $$ ⟨ 110 ⟩ surfaces operating at 200 °C for an hour in a vacuum oven. The highly-oriented $$\langle {110} \rangle $$ ⟨ 110 ⟩ nanotwinned Au films could be an ideal material in many gold products.