ERASABLE PROGRAMMABLE NON-VOLATILE MEMORY
An erasable programmable non-volatile memory includes a first select transistor, a first floating gate transistor, a second select transistor and a second floating gate transistor. A select gate and a first source/drain terminal of the first select transistor receive a select gate voltage and a first source line voltage, respectively. A first source/drain terminal and a second source/drain terminal of the first floating gate transistor are connected with a second source/drain terminal of the first select transistor and a first bit line voltage, respectively. The second select transistor also includes the select gate. A first source/drain terminal of the second select transistor receive a second source line voltage. A first source/drain terminal and a second source/drain terminal of the second floating gate transistor are connected with the second source/drain terminal of the second select transistor and a second bit line voltage, respectively.
This application claims the benefit of U.S. provisional application Ser. No. 62/690,894, filed Jun. 27, 2018, the subject matter of which is incorporated herein by reference.
FIELD OF THE INVENTIONThe present invention relates to a non-volatile memory, and more particularly to an erasable programmable non-volatile memory.
BACKGROUND OF THE INVENTIONAs shown in
The first p-type transistor is used as a select transistor, and the polysilicon gate 34 (also referred as a select gate) of the first p-type transistor is connected to a select gate voltage VSG. The p-type doped region 31 is connected to a source line voltage VSL. The p-type doped region 32 is a combination of a p-type doped drain region of the first p-type transistor and a p-type doped region of the second p-type transistor. The second p-type transistor is a floating gate transistor. The polysilicon gate 36 (also referred as a floating gate) is disposed over the second p-type transistor. The p-type doped region 33 is connected to a bit line voltage VBL. Moreover, the n-type well region (NW) is connected to an n-well voltage VNW.
As shown in
As shown in
As shown in the equivalent circuit of
The select gate of the select transistor receives the select gate voltage VSG. The first source/drain terminal of the select transistor receives the source line voltage VSL. The first source/drain terminal of the floating gate transistor is connected with the second source/drain terminal of the select transistor. The second source/drain terminal of the floating gate transistor receives the bit line voltage VBL. The gate terminal of the n-type transistor and the floating gate of the floating gate transistor are connected with each other. The first source/drain terminal of the n-type transistor and the second source/drain terminal of the n-type transistor are connected with each other to receive the erase line voltage VEL.
SUMMARY OF THE INVENTIONThe present invention provides an erasable programmable non-volatile memory with a novel structure.
An embodiment of the present invention provides an erasable programmable non-volatile memory. The erasable programmable non-volatile memory includes a first select transistor, a first floating gate transistor, a second select transistor and a second floating gate transistor. The first select transistor includes a select gate, a first source/drain terminal and a second source/drain terminal. The select gate of the first select transistor receives a select gate voltage. The first source/drain terminal of the first select transistor receives a first source line voltage. The first floating gate transistor includes a floating gate, a first source/drain terminal and a second source/drain terminal. The first source/drain terminal of the first floating gate transistor is connected with the second source/drain terminal of the first select transistor. The second source/drain terminal of the first floating gate transistor receives a first bit line voltage. The second select transistor includes the select gate, a first source/drain terminal and a second source/drain terminal. The first source/drain terminal of the second select transistor receives a second source line voltage. The second floating gate transistor includes the floating gate, a first source/drain terminal and a second source/drain terminal. The first source/drain terminal of the second floating gate transistor is connected with the second source/drain terminal of the second select transistor. The second source/drain terminal of the second floating gate transistor receives a second bit line voltage. The first select transistor and the first floating gate transistor are constructed in a first well region, the second select transistor and the second floating gate transistor are constructed in a second well region. The first well region and the second well region have different types.
Another embodiment of the present invention provides an erasable programmable non-volatile memory. The erasable programmable non-volatile memory includes a semiconductor layer, a first well region, a first doped region, a second doped region, a third doped region, a second well region, a fourth doped region, a fifth doped region, a sixth doped region, a select gate, a floating gate and an isolation structure. The first well region is formed in the semiconductor layer. The first doped region, the second doped region and the third doped region are formed in a surface of the first well region. The first doped region receives a first source line voltage. The third doped region receives a first bit line voltage. The second well region is formed in the semiconductor layer. The fourth doped region, the fifth doped region and the sixth doped region are formed in a surface of the second well region. The fourth doped region receives a second source line voltage. The sixth doped region receives a second bit line voltage. The select gate is spanned over an area between the first doped region and the second doped region and an area between the fourth doped region and the fifth doped region. The select gate receives a select gate voltage. The floating gate is spanned over an area between the second doped region and the third doped region and an area between the fifth doped region and the sixth doped region. The isolation structure is formed in the semiconductor layer and arranged between the first well region and the second well region.
Numerous objects, features and advantages of the present invention will be readily apparent upon a reading of the following detailed description of embodiments of the present invention when taken in conjunction with the accompanying drawings. However, the drawings employed herein are for the purpose of descriptions and should not be regarded as limiting.
The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which:
As shown in
Three p-type doped regions 21, 22 and 23 are formed in the n-type well region (NW). In addition, a polysilicon gate SG is spanned over the area between the p-type doped regions 21 and 22, and a polysilicon gate FG is spanned over the area between the p-type doped regions 22 and 23. The first p-type transistor is used as a first select transistor, and the polysilicon gate SG (also referred as a select gate) of the first p-type transistor is connected to a select gate voltage VSG. The p-type doped region 21 is connected to a first source line voltage VSL1. The p-type doped region 22 is a combination of a p-type doped drain region of the first p-type transistor and a p-type doped region of the second p-type transistor. The second p-type transistor is used as a first floating gate transistor. The polysilicon gate FG (also referred as a floating gate) is disposed over the second p-type transistor. The p-type doped region 23 is connected to a first bit line voltage VBL1. Moreover, the n-type well region (NW) is connected to an n-well voltage VNW.
Three n-type doped regions 25, 26 and 27 are formed in the p-type well region (PW). In addition, two polysilicon gates SG and FG are spanned over the areas between the three n-type doped regions 25, 26 and 27. The first n-type transistor is used as a second select transistor, and the polysilicon gate SG (also referred as a select gate) of the second n-type transistor is connected to the select gate voltage VSG. The n-type doped region 25 is connected to a second source line voltage VSL2. The n-type doped region 26 is a combination of an n-type doped drain region of the first n-type transistor and an n-type doped region of the second n-type transistor. The second n-type transistor is used as a second floating gate transistor. The polysilicon gate FG (i.e., the floating gate) is disposed over the second n-type transistor. The n-type doped region 27 is connected to a second bit line voltage VBL2. Moreover, the p-type well region (PW) is connected to a p-well voltage VPW.
In this embodiment, the select gate SG of the first select transistor and the select gate SG of the second select transistor are formed of the same polysilicon gate. That is, the select gate SG of the first select transistor and the select gate SG of the second select transistor are connected with each other. Moreover, the floating gate FG of the first floating gate transistor and the floating gate FG of the second floating gate transistor are formed of the same polysilicon gate. That is, the floating gate FG of the first floating gate transistor and the floating gate FG of the second floating gate transistor are connected with each other. Moreover, the channel length L1 of the first floating gate transistor is smaller than the channel length L2 of the second floating gate transistor, and the channel width w1 of the first floating gate transistor is smaller than the channel width w2 of the second floating gate transistor.
As shown in the equivalent circuit of
The first select transistor and the first floating gate transistor are p-type transistors and constructed in the n-type well region (NW). The n-type well region (NW) receives the n-well voltage VNW. The second select transistor and the second floating gate transistor are n-type transistors and constructed in the p-type well region (PW). In addition, the p-type well region (PW) receives the p-well voltage VPW.
The select gate SG of the first select transistor receives the select gate voltage VSG. The first source/drain terminal of the first select transistor receives the first source line voltage VSL1. The first source/drain terminal of the first floating gate transistor is connected with the second source/drain terminal of the first select transistor. The second source/drain terminal of the first floating gate transistor receives the first bit line voltage VBL1.
The select gate SG of the second select transistor receives the select gate voltage VSG. The first source/drain terminal of the second select transistor receives the second source line voltage VSL2. The first source/drain terminal of the second floating gate transistor is connected with the second source/drain terminal of the second select transistor. The second source/drain terminal of the second floating gate transistor receives the second bit line voltage VBL2.
The operations of the erasable programmable non-volatile memory 20 will be described as follows.
During a program cycle of the non-volatile memory 20, the first select transistor and the first floating gate transistor are activated. Consequently, hot carriers (e.g. electrons) are transferred through a channel region of the first floating gate transistor and injected into the floating gate FG.
During an erase cycle of the non-volatile memory 20, the first select transistor and the first floating gate transistor are activated. Consequently, the electrons are ejected from the floating gate FG through the channel region of the first floating gate transistor.
In a read cycle of the non-volatile memory 20, the second select transistor and the second floating gate transistor are activated. According to the amount of electrons in the floating gate FG, the second floating gate transistor generates a read current. According to the magnitude of the read current, the storage state of the non-volatile memory 20 is determined.
As shown in
In the earlier stage of the program cycle, the select gate voltage VSG, the second source line voltage VSL2, the second bit line voltage VBL2 and the p-well voltage VPW are all 0V. Consequently, the second select transistor is turned off. Moreover, the select gate voltage VSG is 0V, the first source line voltage VSL1 is 5V, the first bit line voltage VBL1 is −2V, and the n-well voltage VNW is 5V. In this situation, the first select transistor is turned on, and a program current Ipgm flows through the first select transistor. Consequently, electrons are injected into the floating gate FG through the channel region of the first floating gate transistor.
In the later stage of the program cycle, the second source line voltage VSL2, the second bit line voltage VBL2 and the p-well voltage VPW are all increased to 5V while the select gate voltage VSG is 0V. Consequently, the floating gate FG of the second floating gate transistor is coupled to have the voltage of about 5V. Under this circumstance, more electrons are injected into the floating gate FG of the first floating gate transistor. Consequently, the program efficiency of the non-volatile memory 20 is enhanced.
Please refer to
Since the floating gate FG of the second floating gate transistor is coupled to have the voltage of about −7.5V and both of the first bit line voltage VBL1 and the n-well voltage VNW are 7.5V, a voltage difference between the floating gate FG of the first floating gate transistor and the n-well voltage VNW is 15V. Consequently, the electrons are ejected from the floating gate FG of the first floating gate transistor to the n-type well region (NW).
Please refer to
Generally, the magnitude of the read current Iread is determined according to the amount of electrons stored in the floating gate FG of the second floating gate transistor. For example, in case that electrons are stored in the floating gate FG of the second floating gate transistor, the second floating gate transistor is turned off and the magnitude of the generated read current Iread is very low (e.g., nearly zero). Whereas, in case that no electrons are stored in the floating gate FG of the second floating gate transistor, the second floating gate transistor is turned on and the magnitude of the generated read current Iread is higher. Consequently, the storage state of the non-volatile memory 20 is determined according to the magnitude of the read current Iread.
As mentioned above, the channel length L1 of the first floating gate transistor is smaller than the channel length L2 of the second floating gate transistor, and the channel width w1 of the first floating gate transistor is smaller than the channel width w2 of the second floating gate transistor. Consequently, the program efficiency of the first floating gate transistor is enhanced, and the read efficiency of the second floating gate transistor is enhanced.
Generally, the n-type well region (NW) and the p-type well region (PW) of the non-volatile memory 20 have high doping concentrations. During the erase cycle of the non-volatile memory 20, the n-well voltage VNW is 7.5V and the p-well voltage VPW is −7.5V. That is, the voltage difference between the n-type well region (NW) and the p-type well region (PW) is 15V. If the n-type well region (NW) and the p-type well region (PW) of the non-volatile memory 20 are in contact with each other, the junction breakdown voltage is not enough for sustaining during the erase action. Under this circumstance, a junction breakdown problem occurs.
As shown in
Since the doping concentration of the p-type substrate (p_sub) is low, the junction breakdown voltage between the n-type well region (NW) and the p-type substrate (p_sub) is higher than conventional one. Consequently, during the erase cycle of the non-volatile memory 20, the junction breakdown problem is avoided. However, since the wider isolation structure 29 is formed in the p-type substrate (p_sub), the memory cell of the non-volatile memory 20 has a larger area.
In comparison with the first embodiment, the structures of the well regions of the second embodiment are distinguished. In this embodiment, the n-type well region comprises plural n-type sub-well regions, and the p-type well region comprises plural p-type sub-well regions. For example, the n-type well region comprises three n-type sub-well regions NW1˜NW3, and the p-type well region comprises three p-type sub-well regions PW1˜PW3. In other embodiments, the n-type well region may comprise two n-type sub-well regions or more than three n-type sub-well regions, and the p-type well region may comprise two p-type sub-well regions or more than three p-type sub-well regions.
As shown in
Three p-type doped regions 41, 42 and 43 are formed in the first n-type sub-well region (NW1). In addition, a polysilicon gate SG is spanned over the area between the p-type doped regions 41 and 42, and a polysilicon gate FG is spanned over the area between the p-type doped regions 42 and 43. The first p-type transistor is used as a first select transistor, and the polysilicon gate SG (also referred as a select gate) of the first p-type transistor is connected to a select gate voltage VSG. The p-type doped region 41 is connected to a first source line voltage VSL1. The p-type doped region 42 is a combination of a p-type doped drain region of the first p-type transistor and a p-type doped region of the second p-type transistor. The second p-type transistor is used as a first floating gate transistor. The polysilicon gate FG (also referred as a floating gate) is disposed over the second p-type transistor. The p-type doped region 43 is connected to a first bit line voltage VBL1. Moreover, the n-type well region is connected to an n-well voltage VNW.
Three n-type doped regions 45, 46 and 47 are formed in the first p-type sub-well region (PW1). In addition, two polysilicon gates SG and FG are spanned over the areas between the three n-type doped regions 45, 46 and 47. The first n-type transistor is used as a second select transistor, and the polysilicon gate SG (also referred as a select gate) of the second n-type transistor is connected to the select gate voltage VSG. The n-type doped region 45 is connected to a second source line voltage VSL2. The n-type doped region 46 is a combination of an n-type doped drain region of the first n-type transistor and an n-type doped region of the second n-type transistor. The second n-type transistor is used as a second floating gate transistor. The polysilicon gate FG (i.e., the floating gate) is disposed over the second n-type transistor. The n-type doped region 47 is connected to a second bit line voltage VBL2. Moreover, the p-type well region is connected to a p-well voltage VPW.
During the formation of the well regions, plural ion implantation steps are performed according to different depths. Consequently, the plural n-type sub-well regions and the plural p-type sub-well regions are formed.
Please refer to
Since the doping concentration of the third n-type sub-well region (NW3) and the doping concentration of the third p-type sub-well region (PW3) are low, the junction breakdown voltage between the third n-type sub-well region (NW3) and the third p-type sub-well region (PW3) is very high. Consequently, during the erase cycle, the junction breakdown problem of the non-volatile memory 40 is not generated.
Since the non-volatile memory 40 is not suffered from the junction breakdown problem, the isolation structure 49 in the p-type substrate (p_sub) may be narrower. For example, the width of the isolation structure 49 is smaller than 0.5 μm. After the n-type well region and the p-type well region are formed, the third n-type sub-well region (NW3) and the third p-type sub-well region (PW3) are in direct contact with each other and the junction breakdown problem of the non-volatile memory 40 is avoided.
As mentioned above, the doping concentration of the second n-type sub-well region (NW2) is higher than the doping concentration of the third n-type sub-well region (NW3), and the doping concentration of the second p-type sub-well region (PW2) is higher than the doping concentration of the third p-type sub-well region (PW3). Consequently, the punch through effect between the third n-type sub-well region (NW3) to n-type doped regions 45, 46, and 47 is not generated during the erase cycle.
Since the isolation structure 49 of the non-volatile memory 40 is narrower, the area of the memory cell can be effectively reduced.
Moreover, the threshold voltage of the first select transistor is determined according to the doping concentration of the first n-type sub-well region (NW1), and the threshold voltage of the second select transistor is determined according to the doping concentration of the first p-type sub-well region (PW1). Consequently, the doping concentration of the first n-type sub-well region (NW1) and the doping concentration of the first p-type sub-well region (PW1) are not restricted. The doping concentration of the first n-type sub-well region (NW1) and the doping concentration of the first p-type sub-well region (PW1) may be determined according to the practical requirements.
In the above embodiments, the p-type select transistor and the p-type floating gate transistor are responsible for the program action and the erase action, and the n-type select transistor and the n-type floating gate transistor are responsible for the read action. It is noted that numerous modifications and alterations may be made while retaining the teachings of the invention. For example, in another embodiment, the n-type select transistor and the n-type floating gate transistor constructed in the p-type well region are responsible for the program action and the erase action, and the p-type select transistor and the p-type floating gate transistor constructed in the n-type well region are responsible for the read action.
While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.
Claims
1. An erasable programmable non-volatile memory, comprising:
- a first select transistor comprising a select gate, a first source/drain terminal and a second source/drain terminal, wherein the select gate of the first select transistor receives a select gate voltage, and the first source/drain terminal of the first select transistor receives a first source line voltage;
- a first floating gate transistor comprising a floating gate, a first source/drain terminal and a second source/drain terminal, wherein the first source/drain terminal of the first floating gate transistor is connected with the second source/drain terminal of the first select transistor, and the second source/drain terminal of the first floating gate transistor receives a first bit line voltage;
- a second select transistor comprising the select gate, a first source/drain terminal and a second source/drain terminal, wherein the first source/drain terminal of the second select transistor receives a second source line voltage; and
- a second floating gate transistor comprising the floating gate, a first source/drain terminal and a second source/drain terminal, wherein the first source/drain terminal of the second floating gate transistor is connected with the second source/drain terminal of the second select transistor, and the second source/drain terminal of the second floating gate transistor receives a second bit line voltage,
- wherein the first select transistor and the first floating gate transistor are constructed in a first well region, the second select transistor and the second floating gate transistor are constructed in a second well region, and the first well region and the second well region have different types.
2. The erasable programmable non-volatile memory as claimed in claim 1, wherein the first select transistor and the first floating gate transistor are n-type transistors, and the first well region is a p-type well region that receives a p-well voltage, wherein the second select transistor and the second floating gate transistor are p-type transistors, and the second well region is an n-type well region that receives an n-well voltage.
3. The erasable programmable non-volatile memory as claimed in claim 1, wherein the first select transistor and the first floating gate transistor are p-type transistors, and the first well region is an n-type well region that receives an n-well voltage, wherein the second select transistor and the second floating gate transistor are n-type transistors, and the second well region is a p-type well region that receives a p-well voltage.
4. The erasable programmable non-volatile memory as claimed in claim 1, wherein the first floating gate transistor has a first channel length, and the second floating gate transistor has a second channel length, wherein the first channel length is smaller than the second channel length.
5. The erasable programmable non-volatile memory as claimed in claim 1, wherein the first floating gate transistor has a first channel width, and the second floating gate transistor has a second channel width, wherein the first channel width is smaller than the second channel width.
6. The erasable programmable non-volatile memory as claimed in claim 1, wherein during a program cycle, plural electrons are injected into the floating gate of the first floating gate transistor through a channel region of the first floating gate transistor.
7. The erasable programmable non-volatile memory as claimed in claim 1, wherein during an erase cycle, plural electrons are ejected from the floating gate of the first floating gate transistor to the first well region.
8. The erasable programmable non-volatile memory as claimed in claim 1, wherein during a read cycle, the second floating gate transistor generates a read current.
9. The erasable programmable non-volatile memory as claimed in claim 8, wherein when plural electrons are stored in the floating gate of the second floating gate transistor, the second floating gate transistor generates a first read current, wherein when no electrons are stored in the floating gate of the second floating gate transistor, the second floating gate transistor generates a second read current, wherein the second read current is different from the first read current.
10. An erasable programmable non-volatile memory, comprising:
- a semiconductor layer;
- a first well region formed in the semiconductor layer;
- a first doped region, a second doped region and a third doped region, which are formed in a surface of the first well region, wherein the first doped region receives a first source line voltage, and the third doped region receives a first bit line voltage;
- a second well region formed in the semiconductor layer;
- a fourth doped region, a fifth doped region and a sixth doped region, which are formed in a surface of the second well region, wherein the fourth doped region receives a second source line voltage, and the sixth doped region receives a second bit line voltage;
- a select gate spanned over an area between the first doped region and the second doped region and an area between the fourth doped region and the fifth doped region, wherein the select gate receives a select gate voltage;
- a floating gate spanned over an area between the second doped region and the third doped region and an area between the fifth doped region and the sixth doped region; and
- an isolation structure formed in the semiconductor layer and arranged between the first well region and the second well region.
11. The erasable programmable non-volatile memory as claimed in claim 10, wherein the first well region is a p-type well region that receives a p-well voltage, and the second well region is an n-type well region that receives an n-well voltage, wherein the first doped region, the second doped region and the third doped region are n-type doped regions, and the fourth doped region, the fifth doped region and the sixth doped region are p-type doped regions.
12. The erasable programmable non-volatile memory as claimed in claim 10, wherein the first well region is an n-type well region that receives an n-well voltage, and the second well region is a p-type well region that receives a p-well voltage, wherein the first doped region, the second doped region and the third doped region are p-type doped regions, and the fourth doped region, the fifth doped region and the sixth doped region are n-type doped regions.
13. The erasable programmable non-volatile memory as claimed in claim 10, wherein the first well region, the second doped region, the third doped region and the floating gate are collaboratively formed as a first floating gate transistor, and the second well region, the fifth doped region, the sixth doped region and the floating gate are collaboratively formed as a second floating gate transistor.
14. The erasable programmable non-volatile memory as claimed in claim 13, wherein the first floating gate transistor has a first channel length, and the second floating gate transistor has a second channel length, wherein the first channel length is smaller than the second channel length.
15. The erasable programmable non-volatile memory as claimed in claim 13, wherein the first floating gate transistor has a first channel width, and the second floating gate transistor has a second channel width, wherein the first channel width is smaller than the second channel width.
16. The erasable programmable non-volatile memory as claimed in claim 10, wherein the first well region comprises plural first-type sub-well regions, and the plural first-type sub-well regions are sequentially formed in the semiconductor layer from a surface of the semiconductor layer, wherein the first doped region, the second doped region and the third doped region are formed in a surface of a first one of the first-type sub-well regions of the first well region, wherein the second well region comprises plural second-type sub-well regions, and the plural second-type sub-well regions are sequentially formed in the semiconductor layer from the surface of the semiconductor layer, wherein the fourth doped region, the fifth doped region and the sixth doped region are formed in a surface of a first one of the second-type sub-well regions of the second well region.
17. The erasable programmable non-volatile memory as claimed in claim 16, wherein a last one of the first-type sub-well regions of the first well region and a last one of the second-type sub-well regions of the second well region are in contact with each other.
18. The erasable programmable non-volatile memory as claimed in claim 17, wherein the last one of the first-type sub-well regions of the first well region has a first doping concentration, and a second last one of the first-type sub-well regions of the first well region has a second doping concentration, wherein the second doping concentration is higher than the first doping concentration.
19. The erasable programmable non-volatile memory as claimed in claim 18, wherein the last one of the second-type sub-well regions of the second well region has a third doping concentration, and a second last one of the second-type sub-well regions of the second well region has a fourth doping concentration, wherein the fourth doping concentration is higher than the third doping concentration.
20. The erasable programmable non-volatile memory as claimed in claim 10, wherein the isolation structure is a shallow trench isolation structure.
21. The erasable programmable non-volatile memory as claimed in claim 10, wherein the semiconductor layer is a p-type substrate, an n-type substrate, an n-type buried layer or a deep n-type well region.
Type: Application
Filed: Apr 29, 2019
Publication Date: Jan 2, 2020
Inventor: Chia-Jung HSU (Hsinchu County)
Application Number: 16/397,143