skip to main content


This content will become publicly available on April 28, 2025

Title: Substrate Dependence of the Self-heating in Lead Zirconate Titanate (PZT) MEMS Actuators

Lead zirconate titanate (PZT) thin films offer advantages in microelectromechanical systems (MEMSs) including large motion, lower drive voltage, and high energy densities. Depending on the application, different substrates are sometimes required. Self-heating occurs in the PZT MEMS due to the energy loss from domain wall motion, which can degrade the device performance and reliability. In this work, the self-heating of PZT thin films on Si and glass and a film released from a substrate were investigated to understand the effect of substrates on the device temperature rise. Nano-particle assisted Raman thermometry was employed to quantify the operational temperature rise of these PZT actuators. The results were validated using a finite element thermal model, where the volumetric heat generation was experimentally determined from the hysteresis loss. While the volumetric heat generation of the PZT films on different substrates was similar, the PZT films on the Si substrate showed a minimal temperature rise due to the effective heat dissipation through the high thermal conductivity substrate. The temperature rise on the released structure is 6.8× higher than that on the glass substrates due to the absence of vertical heat dissipation. The experimental and modeling results show that the thin layer of residual Si remaining after etching plays a crucial role in mitigating the effect of device self-heating. The outcomes of this study suggest that high thermal conductivity passive elastic layers can be used as an effective thermal management solution for PZT-based MEMS actuators.

 
more » « less
Award ID(s):
1841453
NSF-PAR ID:
10503396
Author(s) / Creator(s):
; ; ; ; ; ; ;
Publisher / Repository:
AIP PUBLISHING
Date Published:
Journal Name:
Journal of Applied Physics
Volume:
135
Issue:
16
ISSN:
0021-8979
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Perovskite materials, of which strontium titanate (STO) and its thin films are an example, have attracted significant scientific interest because of their desirable properties and the potential to tune thermal conductivity by employing several techniques. Notably, strontium titanate thin films on silicon (Si) substrates serve as a fundamental platform for integrating various oxides onto Si substrates, making it crucial to understand the thermal properties of STO on Si. This work investigates the thermal conductivity of STO thin films on an Si substrate for varying film thicknesses (12, 50, 80, and 200 nm) at room temperature (∼300 K). The thin films are deposited using molecular beam epitaxy on the Si substrate and their thermal conductivity is characterized using the frequency domain thermoreflectance (FDTR) method. The measured values range from 7.4 ± 0.74 for the 200 nm thick film to 0.8 ± 0.1 W m−1 K−1 for the 12 nm thick film, showing a large effect of the film thickness on the thermal conductivity values. The trend of the values is diminishing with the corresponding decrease in the thin film thickness, with a reduction of 38%–93% in the thermal conductivity values, for film thicknesses ranging from 200 to 12 nm. This reduction in the values is relative to the bulk single crystal values of STO, which may range from 11 to 13.5 W m−1 K−1 [Yu et al., Appl. Phys. Lett. 92, 191911 (2008) and Fumega et al., Phys. Rev. Mater. 4, 033606 (2020)], as measured by our FDTR-based experiment. The study also explores the evaluation of volumetric heat capacity (Cp). The measured volumetric heat capacity for the 200 nm thin film is 3.07 MJ m−3 K−1, which is in reasonable agreement with the values available in the literature.

     
    more » « less
  2. Piezoelectric microelectromechanical systems (piezoMEMS) enable dense arrays of actuators which are often driven to higher electrical fields than their bulk piezoelectric counterparts. In bulk ceramics, high field driving causes internal heating of the piezoelectric, largely due to field-induced domain wall motion. Self-heating is then tracked as a function of vibration velocity to determine the upper bound for the drive levels. However, the literature is limited concerning self-heating in thin film piezoMEMS. In this work, it is shown that self-heating in piezoMEMS transducer arrays occurs due to domain wall motion and Ohmic losses. This was demonstrated via a systematic study of drive waveform dependence of self-heating in piezoMEMS arrays. In particular, the magnitude of self-heating was quantified as a function of different waveform parameters (e.g., amplitude, DC offset, and frequency). Thermal modeling of the self-heating of piezoMEMS using the measured hysteresis loss from electrical characterization as the heat source was found to be in excellent agreement with the experimental data. The self-heating model allows improved thermal design of piezoMEMS and can, furthermore, be utilized for functional heating, especially for device level poling. 
    more » « less
  3. null (Ed.)
    Abstract Gallium nitride (GaN) has emerged as one of the most attractive base materials for next-generation high-power and high-frequency electronic devices. Recent efforts have focused on realizing vertical power device structures such as in situ oxide, GaN interlayer based vertical trench metal–oxide–semiconductor field-effect transistors (OG-FETs). Unfortunately, the higher-power density of GaN electronics inevitably leads to considerable device self-heating which impacts device performance and reliability. Halide vapor-phase epitaxy (HVPE) is currently the most common approach for manufacturing commercial GaN substrates used to build vertical GaN transistors. Vertical device structures consist of GaN layers of diverse doping levels. Hence, it is of crucial importance to measure and understand how the dopant type (Si, Fe, and Mg), doping level, and crystal quality alter the thermal conductivity of HVPE-grown bulk GaN. In this work, a steady-state thermoreflectance (SSTR) technique was used to measure the thermal conductivity of HVPE-grown GaN substrates employing different doping schemes and levels. Structural and electrical characterization methods including X-ray diffraction (XRD), secondary-ion mass spectrometry (SIMS), Raman spectroscopy, and Hall-effect measurements were used to determine and compare the GaN crystal quality, dislocation density, doping level, and carrier concentration. Using this comprehensive suite of characterization methods, the interrelation among structural/electrical parameters and the thermal conductivity of bulk GaN substrates was investigated. While doping is evidenced to reduce the GaN thermal conductivity, the highest thermal conductivity (201 W/mK) is observed in a heavily Si-doped (1–5.00 × 1018 cm−3) substrate with the highest crystalline quality. This suggests that phonon-dislocation scattering dominates over phonon-impurity scattering in the tested HVPE-grown bulk GaN substrates. The results provide useful information for designing thermal management solutions for vertical GaN power electronic devices. 
    more » « less
  4. In this study, we compared the transient self-heating behavior of a homoepitaxial β-Ga2O3 MOSFET and a GaN-on-Si HEMT using nanoparticle-assisted Raman thermometry and thermoreflectance thermal imaging. The effectiveness of bottom-side and double-side cooling schemes using a polycrystalline diamond substrate and a diamond passivation layer were studied via transient thermal modeling. Because of the low thermal diffusivity of β-Ga2O3, the use of a β-Ga2O3 composite substrate (bottom-side cooling) must be augmented by a diamond passivation layer (top-side cooling) to effectively cool the device active region under both steady-state and transient operating conditions. Without no proper cooling applied, the steady-state device-to-package thermal resistance of a homoepitaxial β-Ga2O3 MOSFET is 2.6 times higher than that for a GaN-on-Si HEMT. Replacing the substrate with polycrystalline diamond (under a 6.5 μm-thick β-Ga2O3 layer) could reduce the steady-state temperature rise by 65% compared to that for a homoepitaxial β-Ga2O3 MOSFET. However, for high frequency power switching applications beyond the ~102 kHz range, bottom-side cooling (integration with a high thermal conductivity substrate) does not improve the transient thermal response of the device. Adding a diamond passivation over layer diamond not only suppresses the steadystate temperature rise, but also drastically reduces the transient temperature rise under high frequency operating conditions. 
    more » « less
  5. null (Ed.)
    Understanding the failure mechanisms of piezoelectric thin films is critical for the commercialization of piezoelectric microelectromechanical systems. This paper describes the failure of 0.6 mu m lead zirconate titanate (PZT) thin films on Si wafers with different in-plane stresses under large electric fields. The films failed by a combination of cracking and thermal breakdown events. It was found that the crack initiation and propagation behavior varied with the stress state of the films. The total stress required for crack initiation was estimated to be near 500 MPa. As expected, cracks propagated perpendicular to the maximum tensile stress direction. Thermal breakdown events and cracks were correlated, suggesting coupling between electrical and mechanical failure. It was also found that films that were released from the underlying substrates were less susceptible to failure by cracking. It was proposed that during electric field loading the released film stacks were able to bow and alleviate some of the stress. Released films may also experience enhanced domain wall motion that increases their fracture toughness. The results indicate that both applied stress and clamping conditions play important roles in the electromechancial failure of piezoelectric thin films. 
    more » « less