KR100621827B1 - Non-volatile mechanical memory device - Google Patents

Abstract

The present invention relates to a nonvolatile mechanical memory. More specifically, when a voltage is applied to the memory, a non-mechanical memory applies a principle in which charge is stored or released in a capacitor while the moving electrode moves by an electrostatic actuation method. It relates to volatile mechanical memory.

According to the present invention, a nonvolatile flash memory which has a simple structure similar to that of a conventional volatile memory but does not have a leakage current and does not require refreshing can be manufactured.

Nonvolatile Memory, Flash Memory, Mechanical Memory, Semiconductor Transistors, MEMS Switches

Description

Non-volatile mechanical memory device

1A to 1C are circuit diagrams showing a conventional memory device.

2 is a schematic diagram showing the concept of a mechanical memory according to a first embodiment of the present invention;

Fig. 3 is a sectional view showing the structure of the mechanical memory according to the first embodiment of the present invention.

4A to 4C are cross-sectional views illustrating write, erase and read operations of the mechanical memory according to the first embodiment, respectively.

Fig. 5 is a circuit diagram showing a mechanical memory array according to the first embodiment.

6 is a schematic diagram showing the concept of a mechanical memory according to a second embodiment of the present invention.

Fig. 7 is a sectional view showing the structure of the mechanical memory according to the second embodiment of the present invention.

8A to 8C are cross-sectional views illustrating write, erase, and read operations of the mechanical memory according to the second embodiment, respectively.

Fig. 9 is a circuit diagram showing a mechanical memory array according to the second embodiment.

Explanation of symbols on the main parts of the drawings

1, 2: first switch 10, 20: mechanical memory

100 substrate 101 insulating film floating gate

103 control gate 105 insulating film 200 second switch

202: input electrode 204: elastic body 206: moving electrode

208 dimple 300 capacitor 302 substrate

304: insulating film 306: floating gate 400: ground electrode

The present invention relates to a nonvolatile mechanical memory. More specifically, when a voltage is applied to the memory, a non-mechanical memory applies a principle in which charge is stored or released in a capacitor while the moving electrode moves by an electrostatic actuation method. It relates to volatile mechanical memory.

Until now, many kinds of memory devices have been researched, developed and commercialized, and have made much progress in the semiconductor industry. Generally, a memory device is classified into a volatile memory device that loses stored charge when the power is cut off and a non-volatile memory device that retains stored charge even when the power is cut off.

1A to 1C are circuit diagrams showing a conventional memory device.

1A to 1C illustrate a typical volatile memory device (DRAM), a static random access memory (SRAM), and a nonvolatile memory device, respectively, a flash memory.

In the case of DRAM, since a charge is leaked by a leakage current of a metal oxide semiconductor (MOS) transistor after a certain time after charge is stored in a capacitor, an additional element for replenishing the leaked charge is added. The necessity for a refresh circuit is essential, and the higher the integration of memory devices, the greater the problem of such leakage current.

In the case of SRAM, MOS transistors are used in combination without using a capacitor, so there is no leakage current unless the power is cut off. However, SER (soft error rate) is a big problem because it is sensitive to harmful environment such as radiation. Has This requires a separate packaging (packaging) to solve the problem is a cause of increasing the memory cost.

Recently, as demand for mobile products such as mobile phones, digital cameras, PDAs, and camcorders is greatly increased, the demand for nonvolatile memory devices, especially flash memory, is rapidly increasing. As shown in FIG. 1C, the flash memory includes a gate oxide 101, a floating gate 102, a control gate 103, and an intermediate insulating layer ONO-oxide / nitride / oxide 105. have.

The method of storing charge in the floating gate 102 includes a method of hot carrier injection by applying a high voltage to a drain, and a Fowler-Nordheim tunneling by applying a high voltage to the control gate 103. There is a way to inject charge. As described above, the flash memory has a drawback in that power consumption is high because write, erase, and read operations are applied by applying a high voltage of about 20V or more. In addition, the write and erase time is slow, electrical reliability deterioration due to gate oxide degradation, particularly data retention and endurance characteristics are poor and sensitive to external radiation.

In order to solve such a problem of the conventional memory device, a mechanical memory using a micromachined mechanical switch using a micromachining technology as a nonvolatile memory device has recently been researched and developed.

Referring to patents related to the conventional mechanical memory (US Pat. Nos. 4,979,149, 6,054,745, 6,473,361, 6,611,033), the memories are driven by using a cantilever or a membrane as a memory device. Low voltage and fast driving speed has the advantage of low power consumption. In addition, the write and erase operation time is not only fast, but also mechanically driven, there is no degradation of electrical reliability and insensitive to radiation. However, due to the complexity of the structure and process, there is a scaling limit to reduce the density.

The mechanical memory of U.S. Patent No. 6,509,605 or WO 99/63559 also uses a cantilever as a memory element, and when a voltage is applied to the memory, the cantilever is driven by an electrostatic force to charge the floating gate. The cantilever is fixed and held by the stiction between the cantilever and the floating gate when the voltage is stored, released and no voltage is applied.

In particular, a mechanical memory (US Pat. No. 6,509,605 or WO 99/63559), which is structurally similar to the present invention, applies a voltage to a switching electrode to electrostatically drive a cantilever and contacts a floating gate to charge It stores and emits the memory, writes and erases the memory through it, and removes the voltage, and maintains the stored charge by maintaining the contact state by the stiction between the cantilever and the floating gate. The mechanical memory has an additional switching electrode, which not only increases the memory cost but also maintains the contact state by using the stiction, so that mechanical stress is continuously applied to the cantilever and uniform control of all memory cell stations is achieved. This results in deterioration of the reproducibility, uniformity and reliability of the memory device.

The structure and process of the memory is relatively simple compared to the conventional mechanical memory, but since the operation of the memory device is controlled using the stiction, there is a problem that the uniformity, reproducibility and reliability of the memory device decrease due to the increase in mechanical stress have.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has a structure similar to that of DRAM, which is a conventional volatile memory. It is an object of the present invention to provide a nonvolatile mechanical memory device that ultimately blocks leakage current through a mechanical switch, so that stored charge is maintained even when the power supply is cut off.

In addition, the purpose of the present invention is to provide a nonvolatile mechanical memory device that can be used as a satellite memory without additional packaging because SER is low because it is not sensitive to radiation such as SRAM due to mechanical operation of the nonvolatile mechanical memory.

In addition, by using an electrostatic actuator to store the charge in the floating gate, it can have a lower operating voltage than the conventional flash memory, so that the power consumption is low and the driving speed of the electrostatic driver is faster, so that the memory can be written, erased or read. It is an object of the present invention to provide a nonvolatile mechanical memory device which further increases the operation speed.

Another object of the present invention is to provide a highly reliable nonvolatile mechanical memory device without deteriorating electrical reliability such as gate carrier insulation or hot carrier injection, which is a charge storage method of flash memory, and Fowler-Nordheim tunneling.

It is also an object of the present invention to provide a nonvolatile mechanical memory device having a high degree of integration, which is simple in structure and simple in process compared to a conventional mechanical memory, which is advantageous for scaling down.

In addition, the present invention can reduce the memory cost by using a semiconductor substrate without using an additional switching electrode, and by using a conductor electrode on an arbitrary substrate instead of the semiconductor substrate, the memory can be integrated regardless of the type of substrate. In addition, an object of the present invention is to provide a nonvolatile mechanical memory device that can increase the reproducibility, uniformity, and reliability of the memory device by using electrical or mechanical switches.

The present invention for solving the above problems and the first switch; A capacitor for storing charge transferred from the first switch or transferring the stored charge to the switch; And a second switch electrically connected between the first switch and the capacitor, the second switch mechanically opening and closing the transfer of charge between the first switch and the capacitor.

The first switch may be a semiconductor transistor switch including a metal oxide silicon (MOS) transistor or a thin film transistor.

The first switch is characterized in that the mechanical switch including a MEMS (Micro Electro Mechanical System) or NEMS (Nano Electro Mechanical System) switch.

The capacitor includes a first electrode; A second electrode formed to be spaced apart from the first electrode by a predetermined distance; And an insulating layer formed between the first electrode and the second electrode to electrically insulate the first electrode and the second electrode.

The first electrode may be any one of a conductive electrode formed on a conductive semiconductor substrate or a non-conductive substrate.

The insulating film is formed of an oxide film or a nitride film.

The second electrode may be a conductive floating gate.

The floating gate is made of a conductive material including any one of copper (Cu), carbon nanotubes, and polysilicon.

The second switch may be formed at a position spaced apart from the capacitor by a predetermined distance and include a moving electrode contacting the capacitor by an electrostatic force by a voltage applied from the first switch.

The second switch is connected to the moving electrode, the elastic body for returning the moving electrode in contact with the capacitor to its original position by the elastic force; further includes.

The second switch is formed of a material having an elastic force, and when the electrostatic force by the voltage applied from the first switch is lost, it is characterized in that to return to the original position by the elastic force.

The moving electrode is made of a conductive material including any one of copper, carbon nanotubes, and polysilicon.

The elastic body is made of a conductive material containing any one of copper, carbon nanotubes, polysilicon.

One or more dimples having a protruding shape may be formed in a region of the moving electrode in contact with the capacitor.

The height of the dimple is relatively smaller than the distance between the moving electrode and the capacitor.

Hereinafter, an embodiment of a mechanically operating nonvolatile mechanical memory according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a schematic diagram showing the concept of the mechanical memory 10 according to the first embodiment of the present invention. Referring to FIG. 2, a capacitor 300 connected to the first switch 1 made of a semiconductor transistor, as in DRAM, is illustrated. ) Is present, but there is a second switch 200 that mechanically opens and closes the transfer of charge between the first switch 1 and the capacitor 300.

The capacitor 300 is connected to the ground electrode 400 to maintain the ground state in the state of reading or writing data.

The first switch 1 preferably includes a semiconductor transistor including a metal oxide silicon (MOS) transistor or a thin film transistor.

The second switch 200 records data while storing or releasing electric charges while contacting the capacitor 300 by the electrostatic force generated by the voltage applied from the first switch 1.

Therefore, since the leakage current can be prevented by the operation of the second switch 200, compared to the DRAM configured by simply connecting the first switch 1 and the capacitor 300, non-volatile refresh is not required even with a simple configuration. You will be able to create memory.

First embodiment

3 is a cross-sectional view showing the structure of a nonvolatile mechanical memory (hereinafter referred to as "mechanical memory") according to the first embodiment of the present invention.

The second switch 200 does not exist in the DRAM. The second switch 200 is connected to the first switch 1 to store the charge applied from the first switch 1 in the capacitor 300 or to discharge the memory from the capacitor 300. It works as an element.

An input electrode 202 is formed on the second switch 200, and an elastic body 204 having a predetermined elastic force is electrically connected to the input electrode 202 on the input electrode 202 connected to the first switch 1. Is formed.

The moving electrode 206 is connected to the distal end of the elastic body 204 to be movable by the elastic body 204. The first electrode 1 is electrically connected to the moving electrode 206. The moving electrode 206 may be made of a conductive material, and may be made of copper, carbon nanotubes (CNT), polysilicon, or the like.

Meanwhile, when manufacturing the mechanical memory 10 using copper, carbon nanotubes, or polysilicon having elastic force, the elastic body 204 and the moving electrode 206 are integrally formed as the movable electrode 206 having elastic force. It could be produced.

A dimple 208 protruding to a predetermined size is formed on the lower surface of the moving electrode 206.

The input electrode 202, the elastic body 204, the moving electrode 206, and the dimple 208 are used as components of the second switch 200.

The capacitor 300 is formed in a state spaced apart from the second switch 200 by a predetermined distance, and the capacitor 300 includes a substrate 302, an insulating film 304, and a floating gate 306.

The substrate 302 may be made of a conductive semiconductor substrate, or may be used by forming a conductive electrode on a non-conductive substrate. In the case of using a conductive semiconductor substrate, the silicon substrate may be manufactured.

The insulating film 304 may use a silicon oxide film or a nitride film.

The floating gate 306 may be made of polysilicon or made of a conductive material such as copper or carbon nanotubes.

As described above, the capacitor 300 includes the substrate 302, the insulating film 304, and the floating gate 306. However, the capacitor 300 may include the first electrode, the insulating film, and the second electrode to store and discharge charges. Any type of capacitor 300 may be used if present.

In the mechanical memory 10 according to the first embodiment of the present invention, when a voltage greater than a pull-in voltage V _PI is applied to the semiconductor transistor drain electrode of the first switch 1 while the substrate 302 is grounded, Pull-in voltage is applied to the moving electrode 206 through the input electrode 202.

In this case, the capacitance C _air of the capacitor consisting of the moving electrode 206, the air layer, and the floating gate 306 is smaller than the capacitance C _capacitor of the capacitor consisting of the floating gate 306, the insulating film 304, and the substrate 302. Therefore, as most of the voltage is applied between the moving electrode 206 and the floating gate 306, an electrostatic force is generated between the moving electrode 206 and the floating gate 306.

The reason why the capacitance C _air between the moving electrode 206 and the floating gate 306 is smaller than the capacitance C _capacitor between the floating gate 306 and the substrate 302 is that the air layer is more dielectric than the insulating film 304. This is because the dielectric constant is much smaller.

The movable electrode 206 may be in contact with the floating gate 306 while generating an electrostatic force by application of a voltage, and may be any structure as long as it can be restored to its original position by the elastic force. Such a structure is typically a cantilever (cantilever) or a cantilever (sheep cantilever) fixed at both ends.

4A to 4C are cross-sectional views illustrating writing, erasing, and reading operations of the mechanical memory according to the first embodiment, respectively, and describe the operation of the mechanical memory.

<Write operation>

In the write operation of the mechanical memory 10, a voltage equal to or greater than the threshold voltage V _DD is applied to the gate electrode of the first switch 1 including the semiconductor transistor, and a voltage equal to or greater than the pull-in voltage V _PI is applied to the drain electrode. By doing so.

When a voltage equal to or greater than the pull-in voltage is applied to the drain electrode, the pull-in voltage applied to the drain electrode is transmitted to the moving electrode 206 through the source electrode while the first switch 1 is turned on.

The charge is transferred to the floating gate 306 while the movable electrode 206 and the floating gate 306 are contacted by the electrostatic force between the two by the voltage transferred to the movable electrode 206, and the movable electrode 206 and the floating gate are transferred. When the voltage between the 306 is the same, the electrostatic force between the two disappears and separated from each other by the restoring force of the elastic body 204, the charge is continuously stored in the floating gate 306.

When the first switch 1 is turned off by applying a voltage below the threshold voltage to the gate electrode of the first switch 1, the moving electrode 206 is in a floating state and floats with the moving electrode 206. Since the gate 306 continues to maintain the same voltage, charge is still stored between the substrate 302 and the floating gate 306 even when the applied voltage is removed.

<Clear operation>

In order to erase the information stored in the mechanical memory 10, the first switch 1 is turned on, and when a 0 V voltage is applied to the drain electrode, a 0 V voltage is transmitted to the moving electrode 206 through the source electrode. The moving electrode 206 to which a voltage of 0 V is applied is contacted by the electrostatic force with which the floating gate 306 which has been written, that is charged, is discharged, and the charge stored in the floating gate 306 is released when the voltage between them is equal. do. At this time, when the first switch 1 is turned off by applying a voltage below the threshold voltage to the gate electrode of the first switch 1, the moving electrodes 206 are separated from each other and the applied voltage is removed to remove the applied voltage. In addition, the moving electrode 206 and the floating gate 306 maintain the same voltage.

<Read operation>

The read operation of the mechanical memory 10 turns on the first switch 1, applies a voltage between the 0V voltage and the pull-in voltage to the drain electrode, and connects the substrate 302 to the ground electrode 400 to move. It prevents contact by the electrostatic force between the electrode 206 and the floating gate 306, and measures the small signal capacitance between the moving electrode 206 and the floating gate 306 to determine the charge and discharge states of the charge of the floating gate 306. Check it.

The dimples 208 formed in the moving electrode 206 not only prevent stiction at the contact of the moving electrode 206 and the floating gate 306, but also prevent static electricity between the moving electrode 206 and the floating gate 306. The capacitance C _air between the moving electrode 206 and the floating gate 306 is maintained between the floating gate 306 and the substrate 302 by maintaining the minimum spacing between the two by the dimple 208 when in contact. It prevents it from getting larger than its capacitance (C _capacitor ).

In other words, the distance between the moving electrode 206 and the floating gate 306 becomes too short to prevent the C _air from growing so that the moving electrode 206 can contact the floating gate 306 by the electrostatic force.

5 is a circuit diagram illustrating a mechanical memory array according to a first embodiment.

Referring to FIG. 5, one cell of the mechanical memory 10 includes a first switch 1, a second switch 200 connected one by one to the first switch 1, and a capacitor 300 connected to the ground electrode 400. It is arranged in the same structure as the conventional NOR flash memory, and the X-axis addressing is performed by the gate electrode of the semiconductor transistor, and the Y-axis addressing is performed by the drain electrode of the semiconductor transistor.

Second embodiment

6 is a schematic diagram showing the concept of a mechanical memory according to a second embodiment of the present invention.

The mechanical memory 20 according to the second embodiment has the same structure as in the first embodiment, except that a mechanical switch other than a semiconductor transistor is used as the first switch 2. In particular, in the present invention, it is possible to achieve miniaturization and integration by using a MEMS (Micro Electro Mechanical System) switch or a NEMS (Nano Electro Mechanical System) switch.

7 is a cross-sectional view showing the structure of the mechanical memory according to the second embodiment of the present invention.

Referring to FIG. 7, the mechanical memory 20 according to the second embodiment uses a mechanical switch as the first switch 2 instead of the semiconductor transistor of the mechanical memory 10 according to the first embodiment.

According to such a configuration, the mechanical switch is connected to the second switch 200 and the capacitor 300 to record data while applying or removing a predetermined voltage.

The configuration of the second switch 200 and the capacitor 300 is the same except that a mechanical switch is used instead of the semiconductor transistor as compared with the first embodiment. Since the semiconductor transistor also operates as a switch, the overall operation principle is the same even if it is converted into a mechanical switch.

8A to 8C are cross-sectional views illustrating write, erase, and read operations of the mechanical memory according to the second embodiment, respectively.

Instead of the on / off operation of the first switch 1 using the semiconductor transistor in the first embodiment, the first switch 2 is turned on and off while the mechanical switch is used as the first switch 2. Write, erase, and read operations of the mechanical memory 20 are performed in the same manner as in the example.

Also, the second switch 200 including the moving electrode 206 may also use other MEMS electrostatic drivers in addition to the cantilever as in the first embodiment, and may replace any conductive substrate 302 of the fixed capacitor 300. The same result is obtained when a conductor electrode is formed and used on a nonconductive substrate.

In the mechanical memory 20 according to the second embodiment, one or more dimples 208 are formed on the moving electrode 206 in the same manner as in the first embodiment so that the moving electrode 206 and the floating gate 306 are formed. This prevents the sticking between the two electrodes and maintains the minimum gap between the moving electrodes 206 and the floating gate 306 by the dimples 208 when they are in contact with each other by electrostatic force.

9 is a circuit diagram illustrating a mechanical memory array according to a second embodiment.

Referring to FIG. 9, one cell of the mechanical memory 20 may include a first switch 2, a second switch 200 connected to the first switch 2 one by one, and a capacitor 300 connected to the ground electrode 400. ) Is arranged in the same structure as a conventional NOR flash memory, and the X-axis addressing is performed by the gate of the mechanical switch, and the Y-axis addressing is performed by the input unit.

Although the above-described mechanical memory according to an embodiment of the present invention has been described, the scope of the present invention is not limited to such an embodiment, and a right can be easily modified by those skilled in the art. .

As described above, according to the present invention, a nonvolatile flash memory having a simple structure similar to that of a conventional volatile memory but without a leakage current does not need to be produced.

In addition, according to the present invention, there is an effect that can produce a memory that is not sensitive to radiation and can be operated at a lower operating voltage than the conventional flash memory to reduce power consumption.

In addition, by not using hot carrier injection or Fowler-Nordheim tunneling as in flash memory, it is possible to prevent the electrical reliability deterioration by the gate insulating layer destruction.

In addition, the structure is simpler than the conventional mechanical memory, and the process is simple, which is advantageous in size reduction, thereby improving the degree of integration. Since the above-described conductor electrode can be used, unlike conventional memory devices, devices may be integrated regardless of the type of substrate, thereby improving reproducibility, uniformity, and reliability of the memory devices.

Claims (15)

A first switch; A capacitor for storing charge transferred from the first switch or transferring the stored charge to the switch; And a second switch electrically connected between the first switch and the capacitor, the second switch mechanically opening and closing the transfer of charge between the first switch and the capacitor. The method of claim 1, The first switch is a semiconductor transistor switch including a metal oxide silicon (MOS) transistor or a thin film transistor (Thin Film Transistor). The method of claim 1, The first switch is Non-volatile mechanical memory, characterized in that the mechanical switch including a MEMS (Micro Electro Mechanical System) or NEMS (Nano Electro Mechanical System) switch. The method according to any one of claims 1 to 3, The capacitor is A first electrode; A second electrode formed to be spaced apart from the first electrode by a predetermined distance; And an insulating film formed between the first electrode and the second electrode to electrically insulate the first electrode and the second electrode. The method of claim 4, wherein The first electrode Non-volatile mechanical memory, characterized in that any one of a conductive electrode formed on a conductive semiconductor substrate or a non-conductive substrate. The method of claim 4, wherein The insulating film is A nonvolatile mechanical memory, characterized in that formed of an oxide film or a nitride film. The method of claim 4, wherein The second electrode Nonvolatile mechanical memory, characterized in that the conductive floating gate. The method of claim 7, wherein The floating gate Non-volatile mechanical memory, characterized in that made of a conductive material containing any one of copper (Cu), carbon nanotube (poly), polysilicon (poly silicon). The method of claim 1, The second switch is And a moving electrode formed at a position spaced apart from the capacitor by a predetermined distance and contacting the capacitor by an electrostatic force by a voltage applied from the first switch. The method of claim 9, The second switch is And an elastic body connected to the moving electrode and returning the moving electrode in contact with the capacitor to its original position by an elastic force. The method of claim 9, The second switch is The nonvolatile mechanical memory of claim 1, wherein the nonvolatile mechanical memory is formed of an elastic material and returns to its original position by the elastic force when the electrostatic force by the voltage applied from the first switch is lost. The method of claim 9, The movable electrode is made of a conductive material comprising any one of copper, carbon nanotubes, and polysilicon. The method of claim 10, The elastic body is a non-volatile mechanical memory, characterized in that made of a conductive material containing any one of copper, carbon nanotubes, polysilicon. The method according to any one of claims 9 to 13, And at least one dimple having a protruding shape is formed in a region of the moving electrode in contact with the capacitor. The method of claim 14, The height of the dimple is relatively smaller than the distance between the moving electrode and the capacitor.

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