A 32-Mb chain FeRAM with segment/stitch array architecture

This paper demonstrates the 32-Mb chain ferroelectric RAM (chain FeRAM) with 0.2-μm three-metal CMOS technology. A small die size of 96 mm² and a high cell/chip area efficiency of 65.6% are realized not only by the small cell size using capacitor-on-plug technology but also by two key techniques that utilize the three-metal process: 1) a compact memory cell block structure that eliminates plateline area and reduces block selector area and 2) the segment/stitch array architecture which reduces the area of row decoders and plate drivers. As a result, the average cell size shrinks to 1.875 μm², which is smaller than a 0.13-μm SRAM cell, and the chip size is reduced to 70% of the chain FeRAM of conventional configuration with two-metal process. Moreover, a power-on/off sequence suitable to the chain FeRAM is introduced to protect the memory cell data from the startup noise. Compatibility with low-power SRAM is a key issue for mobile applications. The low-standby-current bias generator is introduced and the standby current of the chip is suppressed to 3 μA. The modified address access mode is also adopted to eliminate the need of intentional address transition after the startup of the chip. The chip enable access time was 50 ns and cycle time was 75 ns at 3.0-V V_dd.