A lead zirconium titanium oxide-based ferroelectric nonvolatile memory

A Nonvolatile Ferroelectric Random Access Memory (NVFRAM) based on thin film PZT (Pb (Zr{dollar}sb{lcub}0.54{rcub}{dollar}Ti{dollar}sb{lcub}0.46{rcub}{dollar}) O{dollar}sb3{dollar}) was designed and fabricated in a 4 mm CMOS process. The memory cells consist of PZT thin film capacitors whose reversible spontaneous polarization is used as the memory storage mechanism. Signal processing circuitry consisting of a low-power amplifier and A/D converter was also designed and fabricated for integration with an on-chip PZT-based piezoelectric pressure sensor. Piezoelectric based sensors typically have extremely small and highly sensitive output signals which are difficult to interface with off-chip processing circuitry. These inherent signal deficiencies require on-chip integrated amplification. The design of these systems was based on the integration of PZT thin films with CMOS circuitry using standard CMOS processing techniques. Polycrystalline PZT thin films with a thickness of 3000 A were deposited on the CMOS wafers using a sol-gel spin casting technique. This process produced thin films worthy of NVFRAM implementation; excellent charge storage characteristics (relative dielectric constant of 1300), and good ferroelectric characteristics: coercive voltage of 5 V (E{dollar}sb{lcub}rm C{rcub}{dollar} = 160 kV/cm), saturation voltage of 10 V (E{dollar}sb{lcub}rm SAT{rcub}{dollar} = 320 kV/cm), remnant polarization (P{dollar}sb{lcub}rm R{rcub}{dollar}) of 20 mC/cm{dollar}sp2{dollar} and saturation polarization (P{dollar}sb{lcub}rm SAT{rcub}{dollar}) of 30 mC/cm{dollar}sp2{dollar}.