NVRAM memory cell architecture that integrates conventional SRAM and flash cells

A nonvolatile static random access memory array comprising:

• a plurality of integrated nonvolatile static random access memory circuits arrange in an array of rows and columns and formed on a substrate, said integrated nonvolatile static random access memory circuit comprising:
• a static random access memory cell comprising:
• a latched memory element to retain a digital signal indicative of a data bit, and
• a first access transistor and a second access transistor connected to allow control access of a first bit line and a second bit line to said latched memory element for writing and reading said digital signal to and from said latched memory element,
• said first and second access transistors having control gates in communication with a word line for controlling access of said latched memory element to said first and second bit lines;
• a first nonvolatile memory element in communication with said latched memory element through a first terminal to receive and permanently retain said digital signal from said latched memory element;
• and
• a second nonvolatile memory element in communication with said latched memory element through a first terminal to receive and permanently retain a complementary level of said digital signal from said latched memory element;
• wherein said first nonvolatile memory element and said second nonvolatile memory element are stacked gate nonvolatile memory elements that have a relatively small coupling ratio of capacitance formed by a control gate placed over a floating gate to a total capacitance of said floating gate and said control gate, such that said control gate of said first nonvolatile memory element and said second nonvolatile memory element reguire a program signal is from approximately +15V to approximately +22V for programming and a erase signal from approximately −15V to approximately −22V for erasing.

A method for forming an integrated nonvolatile static random access memory circuit on a substrate comprising the steps of:

• forming a static random access memory cell by the steps of:
• forming a latched memory element on said substrate to retain a digital signal indicative of a data bit,
• forming a first access transistor and a second access transistor on said substrate,
• connecting said first and second access transistors to allow control access of a first bit line and a second bit line to said latched memory element for writing and reading said digital signal to and from said latched memory element, and
• connecting control gates of said first and second access transistors having control gates to be in communication with a word line for controlling access of said latched memory element to said first and second bit lines;
• forming a first nonvolatile memory element on said substrate;
• placing said first nonvolatile memory element in communication with said latched memory element through a first terminal to receive and permanently retain said digital signal from said latched memory element;
• forming a second nonvolatile memory element;
• and
• placing said second nonvolatile memory element in communication with said latched memory element through a first terminal to receive and permanently retain a complementary level of said digital signal from said latched memory element;
• wherein forming said first nonvolatile memory element and forming said second nonvolatile memory element each comprise the step of stacking said control gate over said floating gate such that said first nonvolatile memory element and said second nonvolatile memory element have relatively small coupling ratio of capacitance formed by said control gate placed over said floating gate to a total capacitance of said floating gate and said control gate, such that said control gate of said first nonvolatile memory element and said second nonvolatile memory element require a program signal is from approximately +15V to approximately +22V for programming and a erase signal from approximately −15V to approximately −22V for erasing.