Non-volatile memory having 3D array of read/write elements with vertical bit lines and select devices and methods thereof
View Patent ↗A three-dimensional memory is formed as an array of memory elements that are formed across multiple layers of planes positioned at different distances above a semiconductor substrate. The memory elements reversibly change a level of electrical conductance in response to a voltage difference being applied across them. The three-dimensional array includes a two-dimensional array of pillar lines acting as local vertical bit lines through the multiple layers of planes which together with arrays of word lines on each plane are used to access the memory elements. The three-dimensional memory is formed over a CMOS substrate with an intermediate pillar select layer. The pillar select layer is formed with a plurality of pillar select devices which are switching transistors formed outside the CMOS and serve to switch selected rows of pillar lines to corresponding metal lines on the substrate.
1. A memory including memory elements arranged in a three-dimensional pattern defined by rectangular coordinates having x, y and z-directions and with a plurality of parallel planes stacked in the z-direction over a semiconductor substrate, the memory further comprising:
a plurality of local bit lines elongated in the z-direction through the plurality of planes and arranged in a two-dimensional rectangular array of bit line pillars having rows in the x-direction and columns in the y-direction;
a plurality of word lines elongated in the x-direction across individual planes and spaced apart in the y-direction between and separated from the plurality of bit line pillars in the individual planes, wherein the bit line pillars and word lines cross adjacent each other at a plurality of locations across the individual planes;
a plurality of non-volatile re-programmable memory elements individually connected through circuits between the bit line pillars and the word lines adjacent the crossings thereof;
a plurality of global conductive lines in the y-direction;
a row of pillar select devices in the x-direction below a selected row of bit line pillar in the x-direction arranged to switch the selected row of bit line pillars to corresponding global conductive lines in the y-direction; and wherein:
each pillar select device is a transistor above the semiconductor substrate and vertically aligned to a corresponding bit line pillar in the selected row of hit line pillars in the z-direction; and wherein:
said plurality of parallel planes stacked in the z-direction has a top surface and a bottom surface; and
a word line in a plane is accessed from the top surface via a conductive riser column connected to the word line.
2. The memory of claim 1 , wherein:
said row of pillar select devices in the x-direction is selected by a common select gate along the x-direction.
3. The memory of claim 1 , wherein
each pillar select device is vertically aligned in the z-direction and is controlled by a common select gate surrounding the vertically aligned transistor in the x-y plane.
4. The memory of claim 1 , wherein
said transistor comprises:
a column of polysilicon in the z-direction having first, second and third portions from bottom to top;
the first portion having n+ dopants;
the second portion having p− dopants; and
the third portion having n+ dopants.
5. The memory of claim 4 , wherein
a common select gate is adjacent to and surrounding the second portion in the x-y plane.
6. The memory of claim 1 , wherein the individual memory elements include at least one of a carbon material or a phase change material.
7. The memory of claim 1 , wherein the individual memory elements are characterized by a level of electrical conductance that changes in response to an electrical stimulus applied thereto.
8. The memory as in claim 1 , wherein:
the word lines are low melting-point metal including aluminum or copper.
9. The memory as in claim 1 , wherein:
the word lines are high melting-point metal including titanium.
10. The memory as in claim 1 , wherein the individual memory elements are characterized by including a material that reversibly changes its level of electrical conductance between at least first and second stable levels in response to an electrical stimulus being applied through the first and second conductive lines between which the memory element is connected.
11. A memory including memory elements arranged in a three-dimensional pattern defined by rectangular coordinates having x, y and z-directions and with a plurality of parallel planes stacked in the z-direction over a semiconductor substrate, the memory further comprising:
a plurality of local bit lines elongated in the z-direction through the plurality of planes and arranged in a two-dimensional rectangular array of bit line pillars having rows in the x-direction and columns in the y-direction;
a plurality of word lines elongated in the x-direction across individual planes and spaced apart in the y-direction between and separated from the plurality of bit line pillars in the individual planes, wherein the bit line pillars and word lines cross adjacent each, other at a plurality of locations across the individual planes;
a plurality of non-volatile re-programmable memory elements individually connected through circuits between the bit line pillars and the word lines adjacent the crossings thereof;
a plurality of global conductive lines in the y-direction;
a row of pillar select devices in the x-direction below a selected row of bit line pillar in the x-direction arranged to switch the selected row of bit line pillars to corresponding global conductive lines in the y-direction; and wherein:
each pillar select device is a transistor above the semiconductor substrate and vertically aligned to a corresponding bit line pillar in the selected row of bit line pillars in the z-direction;
said plurality of parallel planes stacked in the z-direction has a top surface and a bottom surface; and
a common select gate for a row of pillar select devices is accessed from the top surface via a conductive riser column connected to the common select gate.
12. The memory of claim 11 , wherein:
said row of pillar select devices in the x-direction is selected by a common select gate along the x-direction.
13. The memory of claim 11 , wherein
each pillar select device is vertically aligned in the z-direction and is controlled by the common select gate surrounding the vertically aligned transistor in the x-y plane.
14. The memory of claim 11 , wherein
said transistor comprises:
a column of polysilicon in the z-direction having first, second and third portions from bottom to top;
the first portion having n+ dopants;
the second portion having p− dopants; and
the third portion having n+ dopants.
15. The memory of claim 14 , wherein
a common select gate is adjacent to and surrounding the second portion in the x-y plane.
16. The memory of claim 11 , wherein the individual memory elements include at least one of a carbon material or a phase change material.
17. The memory of claim 11 , wherein the individual memory elements are characterized by a level of electrical conductance that changes in response to an electrical stimulus applied thereto.
18. The memory as in claim 11 , wherein:
the word lines are low melting-point metal including aluminum or copper.
19. The memory as in claim 11 , wherein:
the word lines are high melting-point metal including titanium.
20. The memory as in claim 11 , wherein the individual memory elements are characterized by including a material that reversibly changes its level of electrical conductance between at least first and second stable levels in response to an electrical stimulus being applied through the first and second conductive lines between which the memory element is connected.