A Small Ripple and High-Efficiency Wordline Voltage Generator for 3-D nand Flash Memories

Abstract

This article presents a small ripple and high-efficiency wordline (WL) voltage generator to supply voltage to the selected/unselected WLs for program and read operation in 3-D NAND Flash memories. With the proposed scheme of dynamic pump clock voltage and frequency scaling, the output ripple voltage can be minimized to reduce the variation of threshold voltage of the memory cells and the efficiency can be improved to save power consumption at the same time. What is more, with the minimized ripple, the requirement for power supply rejection ratio (PSRR) of the high-voltage regulator used to provide low noise WL voltage can be reduced. The proposed WL voltage generator has been fabricated in a 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> triple-well CMOS process and the core chip size is 0.53 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . While operating at a 1.8-V supply, the measurement results show that the ripple voltage is 5.5 mV at 12-V output voltage under the typical 50-pF cap load conditions of 3-D NAND Flash memories. Furthermore, the output ripple hardly varies with the increase of load current. In addition, the maximum power efficiency is 49% at 400 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{A}$ </tex-math></inline-formula> and can be maintained over 30% in the 50–450- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{A}$ </tex-math></inline-formula> current load range.