Memory device and driving method of the memory device

• US 8,854,867 B2
• Filed: 04/09/2012
• Issued: 10/07/2014
• Est. Priority Date: 04/13/2011
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Takemura, Yasuhiko
• Primary Examiner(s): DINH, SON T
• Application Number:
  US13/442,113
• Publication Number:
  US 20120262982A1
• Time in Patent Office: 911 Days
• Field of Search: 365/154, 365/149, 365/49, 365/189.05
• US Class Current: 365/154
• CPC Class Codes: G11C 11/409 Read-write [R-W] circuits
• CPC Class Codes: G11C 11/412 using field-effect transistors only
• CPC Class Codes: G11C 14/0054 in which the volatile element is a SRAM cell

Abstract

A memory device which can reduce power consumption and a driving method thereof are disclosed. In a memory element including an inverter and the like, a capacitor for holding data and a capacitor switching element for controlling store and release of charge in the capacitor are provided. The capacitor switching element is designed so that the off-state current is sufficiently low. Therefore, even when power supply of the inverter is stopped after charge corresponding to data is stored in the capacitor, data can be held for a long period of time. In order to return data, potentials of output and input terminals of the inverter are set to a precharge potential, then charge in the capacitor is released, and power is supplied to the inverter. A switching element for supplying the precharge potential may be provided.

Claims

1. A memory device comprising:

a pair of inverters, wherein an output terminal of one of the phase inversion elements inverters is connected to an input terminal of the other of the inverters, wherein the pair of inverters is configured to hold data when power is supplied;

a capacitor;

a first transistor between the output terminal of the one of the inverters and a terminal, wherein the first transistor is configured to transmit the data between the terminal and the pair of inverters;

a second transistor provided above at least one of the inverters, wherein the second transistor is configured to control a flow of charges between the output terminal of the one of the inverters and the capacitor; and

a circuit, wherein the circuit is configured to set the output terminal of the one of the inverters and an output terminal of the other of the inverters to a first potential.

2. The memory device according to claim 1, wherein the capacitor is provided over at least one of the inverters.

3. The memory device according to claim 1, wherein any one of the inverters is or a clocked inverter.

4. The memory device according to claim 1, wherein the second transistor includes an In—

Ga—

Zn-based oxide semiconductor.

5. The memory device according to claim 1, wherein a hydrogen concentration of a channel formation region of the second transistor is less than or equal to 5×

10¹⁹/cm³.

16. A method for driving the memory device according to claim 1, comprising the steps of:

holding charges in accordance with the data, in the capacitor;

stopping power supply to the pair of inverters;

supplying a first potential to an input terminal and an output terminal of the pair of inverters;

turning the second transistor on; and

supplying power to the pair of inverters.

6. A memory device comprising:

a pair of inverters, wherein an output terminal of one of the inverters is connected to an input terminal of the other of the inverters, wherein the pair of inverters is configured to hold data when power of supplied;

a capacitor;

a first switching element provided above at least one of the inverters, wherein the first switching element is configured to control a flow of charges between the output terminal of the one of the inverters and the capacitor;

a second switching element between input terminals of the pair of inverters; and

a circuit, wherein the circuit is configured to supply a first potential to the input terminal of the one of the inverters.

7. The memory device according to claim 6, wherein the capacitor is provided over at least one of the inverters.

8. The memory device according to claim 6, wherein any one of the inverters is a clocked inverter.

9. The memory device according to claim 6, wherein the first switching element comprises a transistor, and

wherein the transistor includes an In—

Ga—

Zn-based oxide semiconductor.

10. The memory device according to claim 6, wherein the first switching element comprises a transistor, and

wherein a hydrogen concentration of a channel formation region of the transistor is less than or equal to 5×

10¹⁹/cm³.

17. A method for driving the memory device according to claim 6, comprising the steps of:

holding charges in accordance with the data, in the capacitor;

stopping power supply to the pair of inverters;

supplying a first potential to an input terminal and an output terminal of the pair of inverters;

turning the first switching element on; and

supplying power to the pair of inverters.

19. A method for driving the memory device according to claim 6, comprising the steps of:

holding charges in accordance with the data, in the capacitor;

stopping power supply to the pair of inverters;

turning the second switching element on;

supplying a first potential to the input terminal of the other of the inverters;

turning the second switching element off;

turning the first switching element on; and

supplying power to the pair of inverters.

11. A memory device comprising:

a memory element comprising;

a pair of inverters, wherein an output terminal of one of the inverters is connected to an input terminal of the other of the inverters, wherein the pair of inverters is configured to hold data when power is supplied;

a capacitor; and

a first switching element provided above at least one of the inverters, wherein the first switching element is configured to controls a flow of charges between the output terminal of the one of the inverters and the capacitor; and

a second switching element connected to an output terminal of the memory element, wherein the second switching element is configured to control the potential of the output terminal of the memory element.

12. The memory device according to claim 11, wherein the capacitor is provided over at least one of the inverters.

13. The memory device according to claim 11, wherein any one of the inverters is a clocked inverter.

14. The memory device according to claim 11, wherein the first switching element comprises a transistor, and

wherein the transistor includes an In—

Ga—

Zn-based oxide semiconductor.

15. The memory device according to claim 11, wherein the first switching element comprises a transistor, and

wherein a hydrogen concentration of a channel formation region of the transistor is less than or equal to 5×

10¹⁹/cm³.

18. A method for driving the memory device according to claim 11, comprising the steps of:

holding charges in accordance with the data, in the capacitor;

stopping power supply to the pair of inverters;

supplying a first potential to an input terminal and an output terminal of the pair of inverters at a certain potential;

turning the first switching element on; and

supplying power to the inverters.

20. A method for driving the memory device according to claim 11, comprising the steps of:

holding charges in accordance with the data, in the capacitor;

stopping power supply to the pair of inverters;

turning the second switching element on;

supplying a first potential to the input terminal of the other the inverters;

turning the second switching element off;

turning the first switching element on; and

supplying power to the pair of inverters.