Comprehensive erase verification for non-volatile memory

A method of operating non-volatile memory, comprising:

• performing a plurality of programming operations to store user data in a memory system;
• and
• performing a plurality of erase operations to erase said user data, wherein at least one of said erase operations includes the steps of:
• erasing a group of non-volatile storage elements of said memory system;
• performing an erase verification operation to determine whether said group is erased after said step of erasing, said performing includes determining whether a charge at a first portion of said group is above a minimum level,
• reading at least one non-volatile storage element of said group for an erased state, said reading includes determining whether a charge at a second portion of said group is below a maximum level, and
• verifying that said group is erased if said step of performing an erase verification operation determines that said group is erased and said step of reading reads said at last one storage element as erased.

A method of erasing non-volatile memory, comprising:

• erasing a group of non-volatile storage elements during user operation;
• performing an erase verification operation to determine if said group of non-volatile storage elements is erased;
• reading said group of non-volatile storage elements for an erased state, said reading includes applying a first voltage sufficient to turn on an erased storage element to each non-volatile storage element of said group, applying a second voltage at a source side of said group, and applying a third voltage at a drain side of said group, said third voltage is greater than said second voltage;
• and
• verifying that said group is erased if said erase verification operation determines that said group is erased and said step of reading reads said group as erased.

A method of operating non-volatile memory, comprising:

• performing a plurality of programming operations to store user data in a memory system;
• and
• performing a plurality of erase operations to erase said user data, wherein at least one of said erase operations includes the steps of:
• erasing a group of non-volatile storage elements of said memory system;
• performing an erase verification operation to determine whether said group is erased after said step of erasing, said erase verification operation tests conduction in a first direction through said group,
• reading at least one non-volatile storage element of said group for an erased state, said reading tests conduction in a second direction through said group, and
• verifying that said group is erased if said step of performing an erase verification operation determines that said group is erased and said step of reading reads said at last one storage element as erased.