New MFIS structure of sol gel-(Bi,La)/sub 4/Ti/sub 3/O/sub 12/ with silicon nitride buffer layer

Pt/Bi/sub 3.25/La/sub 0.75/Ti/sub 3/O/sub 12//Bi/sub 2/SiO/sub 5//Si/sub 3/N/sub 4//Si MFIS (Metal/Ferroelectric/Insulator/Semiconductor) structures were prepared by sol-gel method. Bi/sub 3.25/La/sub 0.75/Ti/sub 3/O/sub 12/ and Bi/sub 2/SiO/sub 5/ films were deposited at 800/spl deg/C. The Si/sub 3/N/sub 4/ was made by exposing N/sub 2/ radicals to a Si substrate from a radical gun in a vacuum chamber at temperatures from 800/spl deg/C. The MIS diode with this Si/sub 3/N/sub 4/ showed no hysteresis after any thermal treatment. 200 nm-thick Bi/sub 3.25/La/sub 0.75/Ti/sub 3/O/sub 12/ and 10 nm-thick Bi/sub 2/SiO/sub 5/ buffer films were formed by sol-gel method on a 1.8 nm thick Si/sub 3/N/sub 4/ layer. The capacitance-vs-voltage (C-V) characteristic of the MFIS diode showed 1.4 V memory window for the +/-5V voltage scan. The memory window width agreed well with the polarization characteristics (remanent polarization Pr=0.9 /spl mu/ C/cm/sup 2/ and coercive field Ec=40 kV/cm) of a Bi/sub 3.25/La/sub 0.75/Ti/sub 3/O/sub 12/ film, which were measured using a Pt/c-axis-oriented 100 mn-thick Bi/sub 3.25/La/sub 0.75/Ti/sub 3/O/sub 12//Pt capacitor. Moreover, two capacitance values at zero-bias were kept constant for over 24 h, which indicates the retention characteristic of the diode is excellent.