Method for programming a floating gate memory device
DC CAFCFirst Claim
1. A method for programming a floating gate transistor, said floating gate transistor comprising a source, a drain spaced apart from said source, said source and drain being of a first conductivity type and formed in a semiconductor region of a second conductivity type, a channel extending between said source and drain, a floating gate extending over at least a portion of said channel, and a control gate extending over at least a portion of said floating gate, said method comprising the steps of:
- applying a programming voltage to said drain and control gate sufficient to cause hot electron injection programming of said transistor; and
ensuring that the programming drain current for said transistor is less than a predetermined value.
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Abstract
A method of programming a floating gate transistor permits the use of a charge pump to provide drain programming current. The programming drain current is typically held below about 1 μA. This programming drain current can be provided by a conventional charge pump. In the first embodiment, the drain current can be limited by connecting a resistor between the source and ground. In a second embodiment, the drain current is limited by limiting the transistor control gate voltage. In a third embodiment, a charge pump is coupled to the drain while the control gate is repetitively pulsed. Each time the control gate is pulsed, the transistor turns on, and although the drain is initially discharged through the transistor, some hot electrons are accelerated onto the floating gate, and eventually the floating gate is programmed. In these embodiments the erase gate voltage may be raised to enhance programming efficiency.
118 Citations
30 Claims
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1. A method for programming a floating gate transistor, said floating gate transistor comprising a source, a drain spaced apart from said source, said source and drain being of a first conductivity type and formed in a semiconductor region of a second conductivity type, a channel extending between said source and drain, a floating gate extending over at least a portion of said channel, and a control gate extending over at least a portion of said floating gate, said method comprising the steps of:
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applying a programming voltage to said drain and control gate sufficient to cause hot electron injection programming of said transistor; and ensuring that the programming drain current for said transistor is less than a predetermined value. - View Dependent Claims (2, 3, 4, 7, 8, 27, 28)
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5. A method for programming a floating gate transistor, said floating gate transistor comprising a source, a drain spaced apart from said source, said source and drain being of a first conductivity type and formed in a semiconductor region of a second conductivity type, a channel extending between said source and drain, a floating gate extending over at least a portion of said channel, and a control gate extending over at least a portion of said floating gate, said method comprising the steps of:
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applying a programming voltage to said drain; and applying to said control gate a voltage which rises from a first value to a second value such that during the time said voltage at said control gate is rising, electrons are being injected into said floating gate so that the threshold voltage of said transistor increases at a rate which ensures that said transistor does not draw a drain current over a predetermined value during programming. - View Dependent Claims (6)
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9. A method for programming a floating gate transistor, said floating gate transistor comprising a source, a drain spaced apart from said source, said source and drain being of a first conductivity type and formed in a semiconductor region of a second conductivity type, a channel extending between said source and drain, a floating gate extending over at least a portion of said channel, and a control gate extending over at least a portion of said floating gate, said method comprising the steps of:
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applying a programming voltage to said drain and control gate; ensuring that the programming drain current is less than a predetermined value, wherein said step of ensuring comprises the step of providing an electrical resistance between said source and ground, said semiconductor region being grounded. - View Dependent Claims (10, 11, 12, 13)
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14. A method for programming a floating gate transistor, said transistor comprising a source, a drain, a channel extending between said source and drain, a floating gate extending over at least a portion of said channel, and a control gate extending over at least a portion of said floating gate, said method comprising the steps of:
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coupling a programming voltage generator to said drain; and repetitively applying pulses to said control gate to thereby cause hot electron injection programming of said transistor. - View Dependent Claims (15, 16, 17)
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18. A method for programming a floating gate transistor, said transistor comprising a source, a drain, a channel extending between said source and drain, a floating gate extending over at least a portion of said channel, and a control gate extending over at least a portion of said floating gate, said method comprising the steps of:
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coupling a programming voltage generator to said drain; and repetitively applying pulses to said control gate, wherein said programming voltage generator is incapable of generating an output current which said transistor would normally conduct if (1) said floating gate were unprogrammed, (2) said programming drain voltage was applied to said drain, and (3) a programming control gate voltage equal to the amplitude of said pulses was applied to said control gate.
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19. Structure comprising:
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a floating transistor including a source, a drain spaced apart from said source, said source and drain being of a first conductivity type and formed in a semiconductor region of a second conductivity type, a channel extending between said source and drain, a floating gate extending over at least a portion of said channel, and a control gate extending over at least a portion of said floating gate; and means for applying a programming voltage to said drain and control gate to thereby program said transistor by hot electron injection and ensuring that the programming drain current of said transistor is less than a predetermined value. - View Dependent Claims (20, 23, 24, 29, 30)
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21. Structure comprising:
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a floating gate transistor including a source, a drain spaced apart from said source, said source and drain being of a first conductivity type and formed in a semiconductor region of a second conductivity type, a channel extending between said source and drain, a floating gate extending over at least a portion of said channel, and control gate extending over at least a portion of said floating gate; and means for applying a programming voltage to said drain and control gate and ensuring that the programming drain current is less than a predetermined value, wherein said means for applying applies to said control gate a voltage which rises from a first value to a second value such that during the time said voltage at said control gate is rising, electrons are being injected into said floating gate so that the threshold voltage of said transistor increases at a rate which ensures that said transistor does not draw a drain current over said predetermined value during programming. - View Dependent Claims (22)
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25. Structure comprising:
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a floating gate transistor including a source, a drain, a channel extending between said source and drain, a floating gate extending over at least a portion of said channel, and a control gate extending over at least a portion of said floating gate; and means for repetitively applying pulses to said control gate to thereby program said floating gate transistor by hot electron injection. - View Dependent Claims (26)
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Specification