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|Title:||Heteroepitaxial growth of high K dielectric thin films by pulsed laser deposition||Authors:||Yu, Wai-ming||Keywords:||Hong Kong Polytechnic University -- Dissertations
|Issue Date:||2004||Publisher:||The Hong Kong Polytechnic University||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 SiO₂or 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 La₀.₇ Sr₀.₃MnO₃ (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 650°C showed small leakage current density of ~10⁻⁷ Acm⁻ 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 x10⁻⁸ Acm⁻ 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.
|Description:||vii, 102 leaves : ill. ; 30 cm.
PolyU Library Call No.: [THS] LG51 .H577M AP 2004 Yu
|URI:||http://hdl.handle.net/10397/3707||Rights:||All rights reserved.|
|Appears in Collections:||Thesis|
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