Multiphysics devices

• Various FEM and circuit models have been developed to design the devices and investigate the mechanisms of some behaviors. The highly accurate and reliable device models allow us to optimize device performance, reduce development time, and minimize costs. Our design capabilities cover a wide range of RFMEMS resonators and filters, including the film bulk acoustic wave resonators (FBAR), the Lamb wave mode resonators (LWR), the laterally coupled alternative thickness (LCAT) mode resonators and coupled bulk acoustic wave resonators (CBAR) [3-4]. Our special LCAT and CBAR design can achieve both lithographic frequency tunability and high coupling coefficient comparable to FBAR, providing a single-chip solution for integrating filters with different frequencies. A procedure to extract various material parameters by device modelling and fitting with measurements has been established, allowing us to tailor our designs for unique requirements. 
Figure 3. Left: fabricated single-chip acoustic duplexer based on the LCAT resonators [3]; right: fabricated single-chip acoustic duplexer based on CBAR designs [4].
Figure 4. Nonlinear Mason Model for high power analysis of the resonators [5].

• IME has an automatic 8-inch wafer-level RFMEMS device testing platform with RF frequency ranging from 10MHz to 40GHz, high input power up to 40 dBm and wide temperature range from -60 to 300 °C. Besides basic s-parameter testing, the output-input power linearity, one-tone harmonic response and two-tone intermodulation response of the resonators and filters can also be characterized.  

References:
[3] Y. Zhu et al., “AlN based Dual LCAT Filters on a Single Chip for Duplexing Application”, IEEE International Ultrasonics Symposium (IUS), 2018 
[4] C. Liu et al., “Sc0.15Al0.85N-based 4 GHz Coupled Bulk Acoustic Resonators (CBAR) and Filters for the Single-Chip Duplexer Solution”, IEEE International Ultrasonics Symposium (IUS), 2021
[5] Y. Zhang et al., “Experimental and Numerical Study on the Second Order Harmonic (H2) and Third Order Intermodulation Distortion (IMD3) Response of Scandium Aluminum Nitride Based FBAR Devices with Different Scandium Doping Levels”, IEEE International Ultrasonics Symposium (IUS), 2022

• Ferroelectric Random Access Memory (FeRAM) is a type of non-volatile memory that stores data by utilizing the ferroelectric properties of certain materials. Unlike traditional Random Access Memory (RAM), FeRAM does not require power to retain data, making it a suitable option for low-power applications. FeRAM has fast read and write speeds, high endurance, and a long lifespan compared to other non-volatile memory technologies such as Flash Memory, which makes it promising to replace or complement traditional RAM in various applications, including automotive, industrial, and Internet of Things (IoT) devices. IME is developing capacitive FeRAM and ferroelectric tunneling junction (FTJ) devices based on ultrathin ferroelectric HfZrO₂ films (3-10nm) and Al1-xScxN films (20-100nm). Novel approach without high thermal budget has been developed for wake-up of the HfZrO₂ ferroelectricity and improvement of the endurance. As for the Al1-xScxN-based FeRAM devices, high remnant polarization up to over 100 μC/cm2 and steep switching of the polarization can be achieved, enabling high memory window and feasibility of the selector-free FeRAM array. Multiscale device models have been established to understand the polarization switching and leakage in this material, and to simulate the array performance [6]. Further scaling down of the film thickness is under development.
Figure 5. Left: hysteresis loops of ultrathin HfZrO2 films from 3nm to 6nm; right: hysteresis loop of 100nm 30% AlScN film with high remnant polarization and steep switching.

• Conventional computer with separated processor and memory units is suffering from a crucial bottleneck for efficient data movement. On the other hand, innovative computing paradigms such as in-memory computing are intensively studied to further enhance computing energy and time efficiencies toward next milestone. Besides, memory elements with capability of multi-level states per cell with the cross-point array integration forms a promising hybrid memory-computation unit for in-memory computing paradigm. Moreover, analog behavior in ReRAM is also one of the few memory technologies to present synaptic-like programming response as in biological observations, which is an essential building block for neuromorphic computing hardware. IME dedicates to the development of analog memories such as ReRAM and FeRAM so as to achieve high performance and high energy efficiency in-memory computing system. We have showcased the Al₂O₃/Ta₂O₅ based bilayer ReRAM with analog switching characteristics for synaptic applications [7].
Figure 6. Performance of the fabricated Al2O3/Ta2O5 based bilayer analog ReRAM devices.
References:
[6] C. Liu et al., “Multiscale Modeling of Al0.7Sc0.3N-based FeRAM: the Steep Switching, Leakage and Selector-free Array”, IEEE International Electron Devices Meeting (IEDM), 2021  
[7] W. Song et al., “Analog switching characteristics in TiW/Al2O3/Ta2O5/Ta RRAM devices”, Appl. Phys. Lett. 115, 133501 (2019)