Memory device including semiconductor element
View Patent ↗A semiconductor base material stands on a substrate in a vertical direction or extends in a horizontal direction. Between first and second impurity layers disposed at the ends of the semiconductor base material, first and second gate insulating layers and first and second gate conductor layers are disposed around the semiconductor base material. A memory write operation is performed where voltages are applied to the first and second impurity layers and the first and second gate conductor layers to cause an impact ionization phenomenon to occur in a channel region, and among generated groups of electrons and positive holes, the group of electrons are discharged from the channel region and some of the group of positive holes are retained in the channel region. A memory erase operation is performed where the retained group of positive holes are discharged via any of or both of the first and second impurity layers.
1. A semiconductor memory device comprising:
a columnar semiconductor body being extensive for a length and supported by a substrate, the columnar semiconductor body connecting to a first impurity region and a second impurity region located, respectively, at end portions of the length of the columnar semiconductor body, wherein the first and second impurity regions are doped with impurities to have an identical conductivity type;
a first gate conductor layer and a second gate conductor layer formed separately from each other along the length of the columnar semiconductor body and arranged at least partially around the columnar semiconductor body; and
at least one gate insulator provided to insulate the first and second gate conductor layers from the semiconductor columnar body,
wherein the first and second gate conductor layers, the first impurity region and the second impurity region individually provide terminals of the semiconductor memory device, a set of data write biases is applied across the terminals to generate majority carriers, as memory data charges, inside the columnar semiconductor body by either an occurrence of an impact ionization phenomenon or by means a gate-induced drain leakage current, and a set of data erase biases is applied across the terminals to draw the majority carriers out of the columnar semiconductor body.
2. The semiconductor memory device according to claim 1 , wherein a first inversion layer is formed in an outer periphery portion of a first region of the columnar semiconductor body surrounded by the first gate conductor layer to operate the first region in a saturation region and to form a pinch-off point in a vicinity of an end portion of the first inversion layer,
a second inversion layer is formed in an outer periphery portion of a second region of the columnar semiconductor body surrounded by the second gate conductor layer to operate the second region linearly, and
the second inversion layer functions as a drain to cause the impact ionization phenomenon to occur in a boundary between the first inversion layer and the second inversion layer.
3. The semiconductor memory device according to claim 1 , further comprising a first PN junction between the first impurity region and the columnar semiconductor body and a second PN junction between the second impurity region and the columnar semiconductor body, wherein application of the set of data erase biases to the terminal turns the first and second PN junctions into a reverse bias state.
4. The semiconductor memory device according to claim 2 , wherein the first impurity region is connected to a source line, the second impurity region is connected to a bit line, and the first conductor layer and the second conductor layer are connected, separately, to a word line and a first driving control line, and
the set of data write biases or data erase biases is applied to the source line, the bit line, the first driving control line, and the word line to selectively perform a data erase operation or a data write operation.
5. The semiconductor memory device according to claim 4 , wherein the source line is orthogonal to the bit line and the first driving control line in plan view.
6. The semiconductor memory device according to claim 1 , wherein the first gate conductor layer and the columnar semiconductor body have a first gate capacitance between them that is larger than a second gate capacitance between the second gate conductor layer and the columnar semiconductor body.
7. The semiconductor memory device according to claim 6 , wherein the first gate capacitance is made larger than the second gate capacitance by means of any or any combination of:
(a) making a first channel length of the first gate conductor layer longer than a second channel length of the second gate conductor layer;
(b) making a first gate insulator covered with the first gate conductor layer thinner than a second gate insulator covered with the second gate conductor layer; and
(c) making a relative dielectric constant of the first gate insulator larger than a relative dielectric constant of the second gate insulator.
8. The semiconductor memory device according to claim 1 , wherein the first impurity region and the second impurity region are N-type semiconductor layers, and the columnar semiconductor body is a P-type semiconductor layer or a neutral semiconductor layer.
9. The semiconductor memory device according to claim 1 , wherein application of the set of data write biases to the terminals causes a group of positive holes to be generated by the impact ionization phenomenon and stored within the columnar semiconductor body, and
increase of the positive holes stored in the columnar body causes a threshold voltage of the first or second gate conductor layer to decrease in a way that allows a bias applied to either the first or second gate conductor layer to decrease.
10. The semiconductor memory device according to claim 1 , wherein application of the set of data write biases to the terminals causes a group of positive holes to be generated by the impact ionization phenomenon and stored in the columnar semiconductor body, and
increase of the positive holes stored in the columnar semiconductor body causes a current flowing through the columnar semiconductor body to increase, and causes the impact ionization phenomenon to become more significant to enhance data writing by a positive feedback.
11. The semiconductor memory device according to claim 4 , wherein application of the set of data write biases or the set of data read biases to the terminals causes an inversion layer to be formed in the outer periphery portion of the first or second region of the columnar semiconductor body connected to the first driving control line.
12. The semiconductor memory device according to claim 1 , wherein the columnar semiconductor body is formed horizontally along the substrate.
13. The semiconductor memory device according to claim 1 , wherein the columnar semiconductor body is formed perpendicular to the substrate.
14. The semiconductor memory device according to claim 1 , wherein the at least one gate insulator is formed of an identical material to insulate both the first and second gate conductor layers from the semiconductor columnar body.
15. The semiconductor memory device according to claim 1 , wherein the at least one gate insulator is formed of different material layers to insulate the first gate conductor layer and the second gate conductor layer, respectively.
16. The semiconductor memory device according to claim 13 , further comprising a first insulating material layer disposed adjacent to the first gate conductor layer and the second gate conductor layer and configured to extend in a vertical direction relative to the substrate, wherein the first insulating material layer is formed with or without a hole.
17. The semiconductor memory device according to claim 16 , wherein the first insulating material layer is formed of a low-dielectric-constant material.
18. The semiconductor memory device according to claim 13 , further comprising a second insulating material layer disposed adjacent to at least one of a first wiring conductor layer connected to the first impurity region and a second wiring conductor layer connected to the second impurity region, wherein the second insulating material layer is formed with or without a hole.
19. The semiconductor memory device according to claim 18 , wherein the second insulating material layer is formed of a low-dielectric-constant material.
20. The semiconductor memory device according to claim 16 , further comprising a first conductor layer extending in a horizontal direction, wherein the first conductor layer is disposed at a bottom of the first insulating material layer and connected to the first gate conductor layer.
21. The semiconductor memory device according to claim 1 , further comprising a first impurity well layer formed in the substrate, and a second impurity well layer formed in the first impurity well layer,
wherein the columnar semiconductor body is formed on the second impurity well layer in parallel to or in perpendicular to the substrate.
22. The semiconductor memory device according to claim 21 , wherein the substrate is formed of a P-type semiconductor, the first impurity well layer is formed of an N-type semiconductor, and the second impurity well layer is formed of a P-type semiconductor, and
a negative bias is applied to the second impurity well layer when a data erase operation is performed.
23. The semiconductor memory device according to claim 1 , wherein the first gate conductor layer is divided into a plurality of portions, and an identical driving bias or different driving biases are applied to the plurality of portions of the first gate conductor layer, either synchronously or asynchronously.
24. The semiconductor memory device according to claim 1 , wherein the second gate conductor layer is divided into a plurality of portions, and an identical driving bias or different driving biases are applied to the plurality of portions of the second gate conductor layer, either synchronously or asynchronously.