The formation of Al3Sc, in 100 nm Al0.8Sc0.2 films, is found to be driven by exposure to high temperature through higher deposition temperature or annealing. High film resistivity was observed in films with lower deposition temperature that exhibited a lack of crystallinity, which is anticipated to cause more electron scattering. An increase in deposition temperature allows for the nucleation and growth of crystalline Al3Sc regions that were verified by electron diffraction. The increase in crystallinity reduces electron scattering, which results in lower film resistivity. Annealing Al0.8Sc0.2 films at 600 °C in an Ar vacuum environment also allows for the formation and recrystallization of Al3Sc and Al and yields saturated resistivity values between 9.58 and 10.5 μΩ-cm regardless of sputter conditions. Al3Sc was found to nucleate and grow in a random orientation when deposited on SiO2, and highly {111} textured when deposited on 100 nm Ti and AlN films that were used as template layers. The rocking curve of the Al3Sc 111 reflection for the as-deposited films on Ti and AlN at 450 °C was 1.79° and 1.68°, respectively. Annealing the film deposited on the AlN template reduced the rocking curve substantially to 1.01° due to recrystallization of Al3Sc and Al within the film.
This work demonstrated both NbN and Nb make good electrodes for stabilizing orthorhombic phase of Hf0.6Zr0.4O2 ferroelectric films. Wake up are < 100 cycles. Pr can be as high as 30 µC/cm2 - respectively 14 and 18 µC/cm2 here. Further, capacitance suggests an orthorhombic phase can be stabilized. Addition of a linear dielectric under modest thickness can tune the Pr and reduce leakage.
Lundh, James S.; Coleman, Kathleen; Song, Yiwen; Griffin, Benjamin A.; Esteves, Giovanni E.; Douglas, Erica A.; Edstrand, Adam E.; Badescu, Stefan C.; Moore, Elizabeth A.; Leach, Jacob H.; Moody, Baxter; Trolier-Mckinstry, Susan; Choi, Sukwon
In this study, the Raman biaxial stress coefficients KII and strain-free phonon frequencies ω0 have been determined for the E2 (low), E2 (high), and A1 (LO) phonon modes of aluminum nitride, AlN, using both experimental and theoretical approaches. The E2 (high) mode of AlN is recommended for the residual stress analysis of AlN due to its high sensitivity and the largest signal-to-noise ratio among the studied modes. The E2 (high) Raman biaxial stress coefficient of -3.8 cm-1/GPa and strain-free phonon frequency of 656.68 cm-1 were then applied to perform both macroscopic and microscopic stress mappings. For macroscopic stress evaluation, the spatial variation of residual stress was measured across an AlN-on-Si wafer prepared by sputter deposition. A cross-wafer variation in residual stress of ∼150 MPa was observed regardless of the average stress state of the film. Microscopic stress evaluation was performed on AlN piezoelectric micromachined ultrasonic transducers (pMUTs) with submicrometer spatial resolution. These measurements were used to assess the effect of device fabrication on residual stress distribution in an individual pMUT and the effect of residual stress on the resonance frequency. At ∼20 μm directly outside the outer edge of the pMUT electrode, a large lateral spatial variation in residual stress of ∼100 MPa was measured, highlighting the impact of metallization structures on residual stress in the AlN film.
Ferroelectric phase stability in hafnium oxide is reported to be influenced by factors that include composition, biaxial stress, crystallite size, and oxygen vacancies. In the present work, the ferroelectric performance of atomic layer deposited Hf0.5Zr0.5O2 (HZO) prepared between TaN electrodes that are processed under conditions to induce variable biaxial stresses is evaluated. The post-processing stress states of the HZO films reveal no dependence on the as-deposited stress of the adjacent TaN electrodes. All HZO films maintain tensile biaxial stress following processing, the magnitude of which is not observed to strongly influence the polarization response. Subsequent composition measurements of stress-varied TaN electrodes reveal changes in stoichiometry related to the different preparation conditions. HZO films in contact with Ta-rich TaN electrodes exhibit higher remanent polarizations and increased ferroelectric phase fractions compared to those in contact with N-rich TaN electrodes. HZO films in contact with Ta-rich TaN electrodes also have higher oxygen vacancy concentrations, indicating that a chemical interaction between the TaN and HZO layers ultimately impacts the ferroelectric orthorhombic phase stability and polarization performance. The results of this work demonstrate a necessity to carefully consider the role of electrode processing and chemistry on performance of ferroelectric hafnia films.
Fields, Shelby S.; Olson, David O.; Jaszwecki, Samantha T.; Fancher, Chris F.; smith, sean w.; Dickie, Diane U.; Esteves, Giovanni E.; Henry, Michael D.; Davids, Paul D.; Hopkins, Patrick E.; Ihlefeld, Jon F.
Wang, Dixiong W.; Musavigharavi, Pariasadat M.; Zheng, Jeffrey Z.; Esteves, Giovanni E.; Liu, Xiwen L.; Stach, Eric A.; Jariwala, Deep J.; Olsson, Roy H.
In this work, the frequency-dependent ferroelectric properties of 45 nm (Al,Sc)N films sputter deposited on complementary metal–oxide–semiconductor (CMOS)-compatible Al metal electrodes are measured and compared. Low in-plane compressive stress (-10 ± 20 MPa) is observed in (Al,Sc)N thin films deposited on Al electrodes. The (Al,Sc)N films exhibit an imprint in the measured coercive fields (Ec) of -4.3/+5.3 MV cm-1 at 10 kHz. Using positive-up negative-down (PUND) measurements, ferroelectric switching is observed within ≈200 ns of an applied voltage pulse, which demonstrates the ability of ferroelectric (Al,Sc)N to achieve the fast read/write speeds desired in memory devices.
The creation of microelectromechanical systems (MEMS) that can operate through elevated temperatures would enable systems diagnostics and controls that are not possible with conventional-off-the-shelf components. The integration of silicon carbide (SiC) with aluminum nitride (AlN) has led to the fabrication of devices that can withstand elevated temperature anneals >935 °C. The results from a piezoelectric micromachined ultrasonic transducer (PMUT) and a microresonator are reported as demonstrations of the fabrication process. Testing the PMUT response before and after annealing at 935 °C led to a change in resonant frequency of less than 1%, which is attributable to a shift in film stress. The response of the microresonator was RF tested in situ up to 500 °C and showed no degradation in its electromechanical coupling coefficient. The resonant frequency decreased with temperature due to the temperature coefficient of Young's modulus, and the quality factor decreased with temperature and remained unrecoverable upon cooling. The degradation in the quality factor is suspected to be a result of oxidation of the titatium nitride (TiN) top electrode, which increases the resistivity and leads to an unrecoverable reduction in the quality factor. The robust piezoelectric response of AlN at these temperatures show that AlN is a very promising candidate for elevated temperature applications.