Electrical properties of paraelectric (Pb,La)(Nb,Ti)O3 thin films for dynamic random access memory devices

Paraelectric (Pb,La)(Nb,Ti)O3 (PLNT) thin films were deposited by the sol-gel method on (111)Pt/Ti/SiO2/Si substrates at temperatures as low as 600 °C for the use of ULSI (ultralarge scale integration) DRAM (dynamic random access memory) capacitors. Films exhibited a regular polycrystalline cubic perovskite phase and showed the presence of paraelectricity in terms of hysteresis of capacitance–voltage (C–V) and polarization–electric field (P–E) characteristics in metal–insulator–metal (MIM) capacitors. The dielectric constants of the films are 611 for a 200 nm thick film and 619 for a 300 nm thick film in a frequency of 100 kHz. The charge storage density obtained from the polarization measurement for a 200 nm thick film was about 50 fC/μm2, while a leakage current density of 70 nA/cm2 was observed at an applied field of 100 kV/cm. These values qualify the PLNT thin films for an alternate storage node dielectric in DRAM capacitors.