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Two-step Ramp Program Erase Waveform

IP.com Disclosure Number: IPCOM000207253D
Publication Date: 2011-May-23
Document File: 3 page(s) / 38K

Publishing Venue

The IP.com Prior Art Database

Related People

James Yingbo Jia: INVENTOR [+3]

Abstract

A two step ramp erase waveform results in an improved erase time, while still meeting oxide reliability requirements

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Two-step Ramp Program Erase Waveform

Inventors:  James Yingbo Jia; Fethi Dhaoui; Yu Wang

Object of the Invention: To reduce erase/program time in a non-volatile memory; and to reduce oxide stress during ramp for good reliability.

Background of the Invention:  The industry utilizes a single slow ramp, as shown at FIG. 1, so as meet oxide reliability requirements.  Typically:

V_start ranges from 0V to 5V;

V_hold ranges from +/- 8V to +/- 25V depending on erase or program mode;

t1: the ramp time for V_start to V_hold, ranges from ~ 1µs to ~ 10s; and

t2: the holding time at V_hold, ranges from ~ 1µs to ~ 100s.

The above waveform successfully prevents oxide punch through, however results in an extended erase time of no less than 2 µs (total of t1 + t2).  In greater detail, the slope of ramp time t1 is typically selected so as to maintain a constant field on the transistor; and the constant field is set at the maximum that the transistor can withstand for the whole V_hold period, t2, and still fulfill reliability criteria.      

Description of the Invention:  A two step ramp erase waveform results in an improved erase time, while still meeting oxide reliability requirements, as shown in FIG. 2.  In a typical embodiment:

V_start ranges from 0V to 5V;

V_hold ranges from +/- 8V to +/- 25V depending on erase or program mode;

V_2 is an intermediate voltage between V_start and V_hold, which is determined by maximum oxide stress condition;

t1’: the ramp time for the fast ramp from V_start to V_2, limited by circuit capability, range is from sub-µs to 1s;

t1’’: the ramp time for the second ramp from V_2 to V_hold, ranges from ~ 1µs to ~ 10s; and

t2: the holding time at V_hold, ranges from ~ 1µs to ~ 1...