Flash memory cell string
The present invention relates to a flash memory cell string. The flash memory cell string includes a plurality of cell devices and switching devices connected to ends of the cell devices. Each of the cell devices includes a semiconductor substrate, and a transmissive insulating layer, a charge storage node, a control insulating layer and a control electrode sequentially formed on the semiconductor substrate. In the flash memory cell string, a buried insulating layer is provided on the semiconductor substrate between the cell device and an adjacent cell device, thus enabling an inversion layer, which performs the functions of source/drain, to be easily formed. According to the present invention, the reduction characteristics and performance of the cell devices of NAND flash memory are improved, and the inversion layer of a channel is induced through fringing electric fields from the control electrode and the charge storage node if necessary.
1. A flash memory cell string, comprising:
a plurality of sequentially connected cell devices; and
one or more switching devices arranged at ends of the connected cell devices and configured to select a specific cell string,
wherein each of the cell devices comprises:
a semiconductor substrate;
a first semiconductor thin film and a buried insulating layer formed on the semiconductor substrate;
a second semiconductor thin film formed on the first semiconductor thin film and the buried insulating layer;
a transmissive insulating layer, a charge storage node, and a control insulating layer sequentially formed on the second semiconductor thin film; and
a control electrode formed on the control insulating layer,
wherein the buried insulating layer is formed between the first semiconductor thin film and a further first semiconductor thin film of an adjacent cell device, and
wherein the first semiconductor film is formed below the control electrode.
2. The flash memory cell string according to claim 1 , wherein each of the switching devices comprises:
a semiconductor substrate, a first semiconductor thin film, and a second semiconductor thin film identical to those of the cell device;
a gate stack formed on the second semiconductor thin film;
a control electrode formed on the gate stack; and
a source or drain region formed in a region of the second semiconductor thin film located on a side not connected to the cell device.
3. The flash memory cell string according to claim 2 , wherein the gate stack is implemented as a single-layer insulating film, or is composed of a transmissive insulating layer, a charge storage node and a control insulating layer.
4. The flash memory cell string according to claim 2 , wherein the switching device further comprises a buried insulating layer formed in a region of the first semiconductor thin film located on either or both of sides of the control electrode of the switching device.
5. The flash memory cell string according to claim 1 , wherein the first semiconductor thin film has an etching ratio different from that of the semiconductor substrate, and the second semiconductor thin film has an etching ratio different from that of the first semiconductor thin film.
6. A flash memory cell string, comprising:
a plurality of sequentially connected cell devices; and
one or more switching devices arranged at ends of the connected cell devices and configured to select a specific cell string,
wherein each of the cell devices comprises:
a semiconductor substrate;
a first semiconductor thin film and a buried insulating layer formed on the semiconductor substrate;
a second semiconductor thin film formed on the first semiconductor thin film and the buried insulating layer;
a transmissive insulating layer, a charge storage node, and a control insulating layer sequentially formed on the second semiconductor thin film;
a control electrode formed on the control insulating layer; and
source and drain regions formed on the second semiconductor thin film disposed on both sides of the control electrode,
wherein the buried insulating layer is formed between the first semiconductor thin film and a further first semiconductor thin film of an adjacent cell device, and
wherein the first semiconductor film is formed below the control electrode.
7. The flash memory cell string according to claim 6 , wherein the first semiconductor thin film has an etching ratio different from that of the semiconductor substrate, and the second semiconductor thin film has an etching ratio different from that of the first semiconductor thin film.
8. The flash memory cell string according to claim 6 , wherein each of the switching devices comprises:
a semiconductor substrate, a first semiconductor thin film and a second semiconductor thin film identical to those of the cell device;
a gate stack formed on the second semiconductor thin film;
a control electrode formed on the gate stack; and
source and drain regions formed in regions of the second semiconductor thin film disposed on both sides of the control electrode.
9. The flash memory cell string according to claim 8 , wherein the gate stack is implemented as a single-layer insulating layer, or is composed of a transmissive insulating layer, a charge storage node and a control insulating layer.
10. The flash memory cell string according to claim 6 , wherein the source and drain regions of the switching device are doped at a higher density than that of source and drain regions of the cell device.