| The Pb(ZrxTi1-x)O3 (PZT) thin films are potential candidates for ferroelectric random access memory (FeRAM) devices and components for microelectromechanical systems (MEMS). For example, the PZT/GaN system is being explored as RF MEMS devices for insertion in RF communication systems. A reproducible sol-gel process was developed for the deposition of PZT films on wurtzite (0001) GaN/sapphire substrates. The composition, crystallography, and interfacial nanochemistry were evaluated by various characterization techniques. The PZT/GaN heterostructure exhibited a chemically sharp interface with insignificant interdiffusion between PZT and GaN layers. However, PZT in metal -ferroelectric -semiconductor (MFS) configuration showed lower capacitance and asymmetrical polarization hysteresis compared to PZT in metal-ferroelectric-metal configuration. Such a deviation was attributed to the high depolarization field (Edepol) within PZT. To mitigate this issue, a two-pronged approach was used. First, the calculated spatial distribution of the electric field and potential, which stem from all the charge densities within the MFS configuration, demonstrated that by adjusting controllable parameters, one can minimize Edepol and maximize polarization. Second, a robust metal-organic chemical vapor deposition (MOCVD) process was developed to fabricate high quality PZT thin films on GaN. In this experimental approach, phase-pure and highly (111) oriented PZT films were deposited on GaN/sapphire substrates by MOCVD. The orientation relationships of PZT/GaN system were determined using x-ray pole figure and high-resolution transmission electron microscopy (TEM). The nanochemistry of the PZT/GaN interface, studied using analytical TEM, indicated a chemically sharp interface with interdiffusion limited to a region below 5 nm. The properties of MOCVD-PZT on GaN are briefly compared with PZT by sol-gel processing, rf sputtering, and pulsed laser deposition.; Additionally, a preliminary study on the PZT/MOCVD-Ru system was carried out to demonstrate its potential as 3-D metal/PZT/metal stacks for high density FeRAMs. The properties of PZT on as-deposited and RTA-pretreated Ru films were characterized and explained in terms of the evolved nanostructure. The PZT films on as deposited Ru, as opposed to annealed Ru, exhibited improved electrical properties. Moreover, a Ru/PZT/Ru capacitor stack, fabricated by selectively depositing Ru top electrodes on PZT, yielded a symmetric hysteresis loop with high remnant polarization of 40 muC/cm2. |
