Studies On The Key Process And Device Model For Ferroelectric Memory

Nowdays, integrated ferroelectric devices which unite ferroelectric films and silicon based semiconductor integrated circuit chips have attracted much more attention. As one of the most important ferroelectric devices, ferroelectric random access memory (FeRAM) has extensive expectation in the field of future nonvolatility memory device due to its ideal memory properties such as low power consumption, fast access time and anti-radialization. In this work, we carry out researches in the following four topics of major relevance to ferroelectric memory.Taking the ferroelectric and dielectric properties, as well as leakage current into consideration, Pb(Zr,Ti)O3(PZT) film with composition near Morphotropic phase boundary (MBP) is seemed to be an ideal ferroelectric material using in ferroelectric memory. Orthogonal sintering experiments were implemented to obtain high density ceramic target for sputtering. Influence of sputtering parameters on the composition fluctuation of deposited PZT films and the resistivity of deposited BPO electrodes were also studied respectively. Compared to the Pt electrodes, BPO electrodes can improve the ferroelectric fatigue properties of PZT film significantly.20-sin2Ψand Williamson-Hall method were used to investigate the residual stress and microstrain of PZT thin films with composition near MPB region, which were grown on BPO electrodes. The PZT thin film grown on BPO electrodes with thickness of 34nm, 68nm,135nm and 270nm, represented tensile stress. By a simple calculation, we suggest that these tensile stresses mainly originates from the phase transformation stresses. It is also noticed that the magnitude of tensile stresses in our PZT films, which can be adjusted by changing the thickness of BaPbO3 electrodes, is proportional to the sizes of grain. By rietveld analysis method, it is found that a higher content of monoclinic phase can be formed in tensile stress PZT films with composition near MPB region. The monoclinic phase in PZT films of MPB possesses a increased poling efficiency, thus leading to a higher remanent polarization and lower coercive field.Based on the microscopic analysis of ferroelectric film, the mechanism of ferroelectric domain switching under random electrical field was interpreted geometrically. From which, the distribution function of coercive field p(Ec+,Ec-) was derivated, and polarization reversal function was employed to describe the change of polarization value as a function of external field. Device model of ferroelectric capacitor and the approach to embed it into EDA tools were developed. This proposed model can be used not only to optimize the core circuit of ferroelectric device, but also to analyze ferroelectric fatigue as a physical diagnostic tool.Hydrogen barrier technology was studied. Different etching schemes for Al2O3 contact holes formation were compared, and reactive ion etching with CHCI3 gas shows the highest etching rate. Stress matching between Al2O3 barrier layer and the other dielectric layers was estimated. The effect of Al2O3 film serves as the hydrogen barrier layer used in ferroelectric memory was examined, and a only 30nm Al2O3 layer had shown significant improvement on protesting ferroelectric capacitor from forming gas annealing.