Study Of Barium Strontium Titanate, Niobium Strontium Titanate And Ferroelectric Random Access Memory

This dissertation includes three parts of the studies: BSTO, Nb-STO and FeRAM. Reviews of the preperation and characterization of BSTO thin films, Nb-STO ceramic varistor, and multilayer ferroelectric thin films are given. The applications of BSTO on DRAMs and MMICs, Nb-STO on multi-functional devices, and physics of the ferroelectric multilayer structure are discussed. The main contents are as follows:1) Thin Mn doped-BST films have been developed based on a sol-gel method with an aqueous acetate sol-gel method. The I-V properties and dielectric properties show that the leakage currents were 0.1nA/cm2, dielectric losses of Mn(II) doped BST films were 0.01⁰.03, and dielectric constants reached to 800.2) The Nb-SrTiO3 ceramics with new processing arts have a higher nonlinear coefficients ofα= 8¹3, and a lower transition electrical voltage of 0.2².9V mm^-1, which agrees with the operation voltage of IC and LSI. Effective dielectric coefficient (εeff) reaches 4⁹×10⁵, dielectric losses tgδ< 1%, which are lower than reported.3) A novel structure of the FeRAM was proposed based on a systematical and thorough investigation of the memory physics in multilayer film and the works by former two doctors. The following effects are obtained:(1) Low leakage current density. All three structures have very low leakage current density of 10-10A/cm2, which can meet the demands of FeRAM.(2) Built-in voltage. The smaller the slop of the linear voltage drop line declines, the lower the built-in voltage will be; The built-in voltage affects the band bending near the interface, and may cause the asymmetric behaviors, then cause imprint failures and depolarization as well.(3) Capacity retention effects. For C-t curves level out, the depolarization field Edep must be smaller that the coercive field, e.g., ?Vb must be lower than Vc. Ei is corresponding to ?Vb. The Au/BIT/PZT/BIT/p-Si(100) structure has the smallest ?Vb value (0.7 V), which is smaller than its coercive voltage(1.1V). The above three effects prove that the Au/BIT/PZT/BIT/p-Si(100) structure is the best and the only choice for the novel FeRAM.(4) Frequency dispertion effects. The width of depletion near the ferroelectric film increases as the increase of the low-signal frequency at high frequency, and the voltage drop at the interface also increases further. With the extrapolation ofΔV_b from the fitting curve ofΔV_b-frequency and the constrain ofΔV_b<=1.1V, the upper limit of the operation frequency of the Au/BIT/PZT/BIT/p-Si(100) structure can reach to 46MHz.(5) There is a linear relation between the transition voltage VT and the coercive voltage Vc, which is the theoretical foundation for the ferroelectric memory. These relationships are conditions for matching between the I-V loop and the P-V loop and for realizing the readout "1" and readout "0" as well(6) The waveform of writes and reads of the memory of the multiplayer structure is confirmed by the test, which gives a nonvolatile, nondestructive readout...