The challenges and directions for the mass-production of highly-reliable, high-density 1T1C FRAM

The directions to overcome the challenges, which we meet in the mass-production of highly-reliable high-density 1T/1C FRAM, are suggested. Controlling of the wide variations of individual cell signals and the exclusion of the weak cells with tailed cell signals will provide enough sensing signal margin, which is crucial for the safe and reliable operation of 1T/1C FRAM, and are the two key factors for the success of the mass-production of highly-reliable and high-density 1T/1C FRAM. The variations of cell to cell signals have been greatly reduced by improving process uniformity around cells and minimizing the integration-induced degradation of ferroelectric capacitor. The complete screening of weak cells with tailed sensing signals have been achieved by the introduction of the cell test with an external reference voltage. The 64 Mb experimental FRAM with the new processes and the novel test scheme has showed large sensing margins of ∼200mV and excellent reliability properties.