|Title:||Heteroepitaxial growth of high K dielectric thin films by pulsed laser deposition|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
|Department:||Department of Applied Physics|
|Pages:||vii, 102 leaves : ill. ; 30 cm|
|Abstract:||The development of future generation of dynamic random access memories (DRAMs) requires the introduction of new materials with higher dielectric constant than the conventional SiO2 or silicon oxide/nitride based systems. [Pb(Mg1/3Nb2/3)O3]1-x-[PbTiO3]x(PMN1-xPTx) is one of the promising insulator materials for DRAM capacitors. PMN1-xPTx films are attractive for scaling down capacitors in ultralarge scale integrated (ULSI) circuits because of their high dielectric constant, low dielectric loss and low leakage current. The main objective of our study is to fabricate PMN1-xPTx based heterostructures with good electrical properties that satisfy the above-mentioned requirements of future ULSI. The effects of the use of different electrode materials and PbTiO3 (PT) buffer layer on the structural and electrical properties, and surface morphology of PMN0.9PT0.1, have been investigated. Our studies began with growing PMN1-x-PTx thin films on conducting La0.7Sr0.3MnO3 (LSMO) oxide electrodes using LaA1O3 (LAO) (100) single crystal substrates. A novel "split-target" pulsed laser deposition technique was used to fabricate films with x = 0.00, 0.10, 0.35, 0.53 and 1.00. The structural characteristics of the PMN1-xPTx/LSMO/LAO(100) heterostructures were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Crack-free PMN1-x-PTx films were cube-on-cube epitaxially grown on LAO (100) single crystal substrates. Electrical measurement was performed with 0.2-mm diameter patterned Au top electrodes. A maximum dielectric constant of 1554 with dielectric loss of 0.05 was obtained in PMN0.9-PT0.1 films at 10 kHz. The dielectric constant of PMN1-x-PTx films as a function of frequency and temperature was also studied. Special attention was directed towards PMN1-x-PTx with x = 0.10 (largest dielectric constant at room temperature) and 0.35 (Morphotropic Phase Boundary (MPB) composition). All PMN1-x-PTx films grown at 650C showed small leakage current density of ~10-7Acm-2 at 1V. In order to suppress the leakage current of PMN1-x-PTx films, BaPbO3 (BPO) was chosen to make the top/bottom electrodes. The heterostructures based on PMN0.9-PT0.1 were grown on MgO (100) single crystal substrates. Their electrical properties were compared with those using LSMO bottom electrode. Structural investigation by XRD revealed that the PMN0.9-PT0.1 films and BPO layers were cube-on-cube epitaxially grown on lattice matched MgO (100) substrates. Crack-free and closely-packed-grain surface morphology was confirmed by SEM. More importantly, it was found that an optimal case was occurred in Au/PMN0.9PT0.1/BPO/MgO (100) heterostructure. A much reduced leakage current density of 3.26 x10-8Acm-2 at 1 V was obtained. At the same time, the dielectric constant of 1640 and dielectric loss of 0.086 at 10 kHz similar to those of PMN0.9PT0.1 films grown on LSMO electrodes, were maintained. Another parallel study was focused on the enhancement of dielectric constant of the PMN0.9-PT0.1 films by means of utilizing a pre-deposited thin (30nm) PT buffer layer. XRD confirmed that the PMN0.9PT0.1, PT and LSMO films were cube-on-cube epitaxially grown on LAO (100) single crystal substrates. Crack-free and densely-packed-grain of PMN0.9-PT0.1 film surface was again obtained. It was found that an introduction of a 30-nm thick PT buffer layer raised the dielectric constant of PMN0.9PT0.1 to 2309, corresponding to a 50% increase over those without a PT buffer layer.|
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