Study Of Memory In Multilayer Ferroelectric Films

This dissertation includes a review of ferroelectric thin films and ferroelectric memories and measurement investigation on sintering technology of ferroelectric ceramics, modified bismuth titanate (BNT) films, preparing of multilayer ferroelectric thin films, analysised the crystal phase, as well as studyed on the electrical characterization at the interface of multilayer ferroelectric thin films. The main contents are as follow: 1)PZT and BNT ferroelectric ceramics were prepared with special solid-synthesis. The effects of sintering technology on the crystal phase of BNT were investigated using XRD and SEM. The P–E hysteresises were measured using RT66.The results indicated that the high quality BNT ceramics which have good ferroelectric characteristics can be obtained by pre-sintering at 800℃ for 2 hours, and sintering at 1100℃ for 12 hours. 2)The mechanism depositing of ferroelectric thin films in situ at low temperature was discussed. The preparing techniques for Multilayer ferroelectric thin films were studied and BIT, PZT/BIT and BIT/PZT/BIT ferroelectric films were deposited on p-Si(100) substrates successfully. After studied the film quality, morphology and the P-E hysteresises of these three Multilayer ferroelectric thin films, we concluded that the ferroelectric thin films we prepared havde good ferroelectric properties. 3 ) Highly c-axis oriented neodymium-modified bismuth titanate BNT were successfully grown on p-SiO2 substrates by pulsed excimer laser deposition. After examining ferroelectric properties of the c-axis oriented BNT film capacitors as a function of the Nd content, we concluded that the capacitor with x=0.80 had the largest remanent polarization. The remanent polarization (Pr) and the coercive field (Ec) of Bi42xNdxTi3O12 film were 27μC/cm2 and 70kV/cm at an applied voltage of 10V, respectively. More importantly, the Au/ BNT/p-Si(100) capacitor exhibited fatigue-free behavior up to 1010 read/write switching cycles at a frequency of 1MHz. 4)The very thin films of PZT and BIT were prepared successfully on p-silicon wafer using scanning excimer laser. SEM and X-ray diffraction methods are used for the analyses of microstructure and the temperature characteristic of I-V curves of the very thin films Au/PZT/p-Si(100)and Au/BIT/p-Si(100) are discussed.. The results of the fitting curve show that, in the negative temperature region, I-V curves shows the dependence on the relation between current I and temperature T, but the I-T curve is different from the temperature dependence of ohmic current. And in the positive temperature region, the current I is independent of temperature T, it should be followed by a second square law region corresponding to trap limit spaced charge conduction (SCLC). 5)A modified empirical power law I=A(ξV)n and an approximate formula of I-V curve of the multilayer ferroelectric thin films have been built up. It consists of the coefficient of nonlinearity of I-V curve n and the parameter charactering the voltage drop of the interface, ξ. The voltage drop at the interface, Vi, obtained from the empirical power law and the approximate calculation of the I-V curve is consistent with that obtained form the C-V curve theory. 6)After calculated the voltage trop at interface of the multilayer ferroelectric films. The results show that, the voltage trop of interface are related with the measured capacity, the capacity of ferroelectric films and the capacity of the depletion layer. The voltage trop at interface of the BIT/ PZT/BIT structure is the minimum among the three structures and its interface effect is better than two others. 7)The built –in voltages at the interface of the multilayer ferroelectric films were discussed. Three structure capacitors have three different ΔVb, Among the three structures ,theΔVb, of the Au/BIT/PZT/TBIT/p-Si(100)is the smallest and the ΔVb of the Au/BIT/p-Si(100) is the largest, the value of Au/PZT/TBIT/p-Si(100) is about the same of Au/PZT/p-Si(100). The asymmetric degree of rectification behavior of I-V curve, and an in imprint failure of P-V loop of Au/BIT/PZT/TBIT/p-Si(100) were the smallestand that of the Au/BIT/p-Si(100) were the largest。 8)A new ferroelectric mennory diode (FMD) has fabricated. Au/BIT/PZT/BIT/Si were deposited using pulsed excimer laser. The hysterestic loop, C-V curve, I-V curve and dlog(I)/dlog(v) characteristic curve of this FMD were obtained. The relationship between the transition voltage of the I-V curve of the ferroelectrics and the coercive field of the P-V hysteretic curve has been calculated, the transition voltage of I-V curve of the ferroelectrics is the function of the coercive field of the ferroelectrics. It will be the foundation of a new ferroelectric memory operated by the I-V characteristics. The nonvolatile and nondestructive readout memory waveform is presented.