Electrically erasable programmable read only memory
AssigneeNational Semiconductor Corporation
InventorChenming Hu
Life of this patent
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Abstract
An Electrically Erasable Programmable Read-Only Memory (EEPROM) requires only a single voltage applied to a single control gate for both erasing and writing operations. Writing is accomplished by hot channel electron injection to charge the floating gate of a selected device with electrons. Nonselected devices are kept from charging by either floating their sources or grounding their gates. Devices are erased by grounding the source and drain regions and causing the electrons stored in the floating gates to tunnel to the control gate. Preferred ratioing of the intra-device capacitances prevents erasure of nonselected devices during writing.
Claims15
An EEPROM memory array of floating gate field effect semiconductor devices, each device having a floating gate and a control gate modulating conduction in a channel between source and drain regions, the devices organized in a matrix of columns and rows, the sources of devices on each column coupled to a common column conductor, the control gates of devices on each row coupled to a common row conductor, and the drains of all devices coupled to a common drain conductor, the array further comprising:
- means for sensing conduction in the semiconductor devices;
- and
- means for selectively floating common column conductors so as to program the array.
A method for operating an EEPROM memory array of the type having floating gate field effect semiconductor devices arranged in rows and columns with the sources of devices in each column coupled to a common column conductor and the control gates of the devices in each row coupled to a common row conductor and all the drains connecting to a common drain;
- the method comprising the steps of:
- charging a selected device by applying a first voltage to the common drain, applying a second voltage to the common row conductor of the selected device, applying a ground voltage to the other common row conductors, applying a ground voltage to the common column conductor of the selected device, and floating the other common column conductors;
- reading the selected device by applying a third voltage to the common row conductor of the selected device, applying a fourth voltage between the common source conductor and the drain of the selected device, and detecting the current flowing through the selected device, and
- erasing the selected device by applying the second voltage to the control gate and applying the ground voltage to the drain and source.
Dependencies are inferred from the claim text.