KR20080104935A - Non-volatile memory device of using semiconductor quantum dot - Google Patents

Abstract

A nonvolatile optoelectronic memory device is provided to minimize the power consumption by using only optical signal. A nonvolatile memory device comprises the substrate(100), the source/drain region(120), and the gate electrode(140). The source/drain region is formed on the top of the substrate. The gate electrode is formed on the upper part of channel region between the source/drain areas. The gate electrode varies the threshold voltage according to the optical signal irradiated. The gate electrode comprises the dielectric layer(142), and the transparent electrode layer(144). The dielectric layer is formed on the upper part of the channel region and has the semiconductor quantum dot(143). The transparent electrode layer is formed on the dielectric layer upper part and the optical signal is transmitted.

Description

Non-volatile Memory Device of using Semiconductor Quantum Dot

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to nonvolatile memory devices, and more particularly to nonvolatile optoelectronic memory devices that use optical signals during program and erase operations of data.

A nonvolatile memory device using a semiconductor quantum dot is a memory device in which a floating gate is replaced with a quantum dot, and has a structure in which electrons or holes are tunneled into the semiconductor quantum dot by applying a high voltage to the control gate. The threshold voltage of the MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is changed by tunneling electrons or holes, and the operating principle is that information is programmed or erased by the change of the threshold voltage. There are a number of patents on the EEPROM (Electrically Erasable Programmable Read Only Memory) that uses electrical signals in the tunneling operation of electrons or holes, and are currently commercially available. However, the technology for the memory device using the optical signal is still insignificant.

US Pat. No. 5,936,258 discloses a technique for fabricating a passive matrix type memory device using a GaAs substrate. That is, a quantum dot is disposed between a p-type semiconductor layer and an n-type semiconductor layer to perform light writing by irradiating light using a means such as an optical fiber. The patent basically has a configuration of a p-n junction diode. Therefore, there is a certain distance from the operation of storing or reading data through the transistor.

US Pat. No. 6121474 uses a photon to perform a program operation and changes the threshold voltage of the transistor by trapping charge. To this end, the patent forms nanocrystals in the control layer and forms an insulating layer that wraps around the approximately spherical nanocrystals.

The above patents use an optical signal during a program operation but an electrical signal during a read operation. However, there is a disadvantage that recorded data is easily lost by light and requires a very difficult manufacturing process in terms of forming spherical nanocrystals and the like.

An object of the present invention for solving the above problems is to provide a nonvolatile memory device that can implement high data retention and low power consumption.

The present invention for achieving the above object, a substrate; Source / drain regions formed on the substrate; And a gate electrode formed on the channel region between the source and drain regions, wherein the gate electrode changes a threshold voltage according to an irradiated optical signal.

In addition, the above object of the present invention, the substrate; Source / drain regions formed on the substrate; A gate electrode formed over the channel region between the source / drain regions, the gate electrode comprising: a dielectric layer formed over the channel region and having semiconductor quantum dots; And a conductive transparent electrode layer formed on the dielectric layer and transmitting an optical signal, and a write and erase operation is performed as the optical signal is irradiated to the semiconductor quantum dot. do.

According to the present invention as described above, the write operation and the erase operation are performed by the optical signal passing through the transparent electrode layer of the gate terminal. In addition, while the conventional flash memory applies a high voltage in write and erase operations, the nonvolatile memory device of the present invention uses only an optical signal, thereby minimizing power consumption. In addition, when the optical signal is not applied, the recorded data is not changed, so that stability of high data retention can be ensured.

As the inventive concept allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the drawings, similar reference numerals are used for similar elements.

When a component is referred to as being "top" or "bottom" of another component, it should be understood that other components may be present in between, although they may be formed directly on the other component.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, action, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention.

1 is a cross-sectional view illustrating a nonvolatile memory device according to a preferred embodiment of the present invention.

Referring to FIG. 1, the nonvolatile memory device according to the present exemplary embodiment includes a substrate 100, a source / drain region 120, and a gate electrode 140.

The substrate 100 may be any material having semiconductor characteristics, but it is preferable that a silicon substrate which is already commercialized is used.

In addition, the source / drain regions 120 are doped with n + or p +. If the nonvolatile memory device is n-type, the source / drain region 120 is doped with n +. If the nonvolatile memory device is p-type, the source / drain region 120 is doped with p +.

In addition, a gate electrode 140 is formed on the channel region between the source / drain regions 120. The threshold voltage of the gate electrode 140 is changed by an optical signal. To this end, the gate electrode 140 has a dielectric layer 142 and a transparent electrode layer 144.

In particular, the dielectric layer 142 includes a semiconductor quantum dot 143 therein. Therefore, the dielectric layer 142 has a structure formed to surround the semiconductor quantum dot 143 therein. The dielectric layer 142 is at least one selected from the group consisting of silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, aluminum nitride, magnesium oxide, hafnium oxide, silicon carbide, zinc oxide and gallium nitride, or Alq3. And at least one selected from the group consisting of poly (4-methyl styrene), polyacryl, parylene, polymethyl methacrylate, polystyrene, polyvinylphenol (PVP) and polyethylene terephthalate (PET).

In addition, any of the semiconductor quantum dots 143 may be used as long as the material has semiconductor characteristics. For example, the semiconductor quantum dot 143 is preferably composed of Si, Ge, ZnO, GaN, CdSe, PbS, InP, CdS, ZnSe or GaAs.

The transparent electrode layer 144 may be any conductive material through which an optical signal can be transmitted. Accordingly, the transparent electrode layer 144 may be a transparent conducting oxide (TCO), a nitride compound, or a metal thin film. When TCO is used as the transparent electrode layer 144, the selectable materials include Ga-In-Sn-O, Zn-In-Sn-O, Ga-In-O, Zn-In-O, In-Sn-O , Zn-Sn-O, Mg-In-O, Ga-Zn-O or Al-Zn-O and the like can be selected. In addition, when the nitride compound is used as the transparent electrode layer 144, a selectable material may be TiN or GaN. In addition, when the metal thin film is used as the transparent electrode layer 144, Ni, Pt, Pb, Au, Ti, Al, In, Ca, or a compound thereof may be selected as the selectable material.

The method of forming the semiconductor quantum dot 143 in the dielectric layer 142 is largely divided into two methods.

First, the semiconductor quantum dots 143 are formed simultaneously with the dielectric layer 142. For example, the dielectric layer 142 may be formed of silicon nitride, and the semiconductor quantum dot 143 may be formed of amorphous or crystalline silicon. First, a silicon source gas and a nitrogen source gas are supplied at a ratio of 1: 100 to 1: 5000, and a thin film is deposited at a temperature of 100 ° C. to 700 ° C. in a pressure range of 0.01 tor to 10 tor. The deposition forms a plurality of amorphous or crystalline silicon quantum dots inside the silicon nitride. This is disclosed in the applicant's registered patent No. 422504.

In particular, a technique of simultaneously forming the semiconductor quantum dots 143 and the dielectric layer 142 may be useful when the dielectric layer 142 includes silicon.

Second, the dielectric layer 142 and the semiconductor quantum dot 143 are alternately formed.

That is, the dielectric layer 142 is first doped to form one dielectric layer 142, and the semiconductor quantum dot 143 is formed on the formed dielectric layer 142. If the formation of the semiconductor quantum dots 143 having a plurality of layers is desired, the formation of the dielectric layer 142 and the formation of the semiconductor quantum dots 143 may be alternately performed. Finally, the semiconductor quantum dots 143 are formed in the dielectric layer 142 by forming the dielectric layer 142 filling the upper semiconductor quantum dots 143.

This is a method that can be usefully used when the semiconductor quantum dot 143 is formed in multiple layers in the dielectric layer 142.

FIG. 2 is an energy band diagram for describing a write operation of the nonvolatile memory device shown in FIG. 1.

Referring to FIG. 2, a dielectric layer 142 and a transparent electrode layer 144 having a plurality of semiconductor quantum dots 143 distributed thereon are sequentially stacked on the substrate 100. In addition, the stack of the substrate 100, the dielectric layer 142, the semiconductor quantum dots 143, the dielectric layer 142, and the transparent electrode layer 144 forms a junction on an energy band diagram. In particular, the energy band has an overall curved shape between the substrate 100 and the transparent electrode layer 144 due to the relative positions of the conduction band and the valence band with respect to the Fermi energy EF change due to the bonding between these regions. In addition, when assuming thermal equilibrium throughout the junction, the Fermi energy level EF remains constant throughout the entire region.

The potential barrier, which appears through the overall bending of the energy band described above, is referred to as the internal potential difference Vbi.

The write operation is performed by irradiating the semiconductor quantum dot 143 with an optical signal having an energy of h v1 through the transparent electrode layer 144. In addition, the energy of hv1 is set to be larger than the energy band gap of the semiconductor quantum dot 143. This is because the energy required to form the electron-hole pairs from the semiconductor quantum dots 143. When an optical signal having an energy of hv1 is irradiated, an electron-hole pair is formed in the semiconductor quantum dot 143 through an excitation process between the valence band and the conduction band. The formed electrons and holes are forced in different directions by the internal potential difference. That is, a force that tunnels to the transparent electrode layer 144 due to the internal potential difference acts on the electrons of the conduction band, and a force that tunnels to the substrate 100 due to the internal potential difference acts on the hole of the valence band. At this time, since the effective mass of the electron is smaller than the effective mass of the hole, the probability that the electron is tunneled becomes higher than the probability that the hole is tunneled. This means that there are more electrons tunneling the dielectric layer than holes, and the semiconductor quantum dot 143 is charged with a positive voltage by a plurality of holes.

When the semiconductor quantum dot 143 is charged with a positive voltage and the source / drain is doped with n +, the threshold voltage of the nonvolatile memory is reduced. That is, the voltage applied to the transparent electrode layer 144 to form a channel in the channel region of the nonvolatile memory is reduced. This is called a write operation in the present invention.

FIG. 3 is an energy band diagram for explaining an erase operation of the nonvolatile memory device shown in FIG. 1.

Referring to FIG. 3, an erase operation is performed by irradiating a semiconductor quantum dot 143 through an optical signal having an energy of h v2 through the transparent electrode layer 144. That is, the optical signal having the energy of hv2 is irradiated to the semiconductor quantum dot 143 through the transparent electrode layer 144, and holes present in the valence band are transferred to the excited level (Intraband Excitation). The energy hv2 of the optical signal has a value lower than the optical signal hv1 used for the writing operation and has a value lower than the energy band gap of the semiconductor quantum dot 143. This is because when the optical signal having the energy hv2 is larger than the energy bandgap of the semiconductor quantum dot 143, an electron-hole pair is formed, and newly formed holes are collected in the semiconductor quantum dot 143 so that an erase operation is not performed. Therefore, the energy hv2 of the optical signal required for the erase operation becomes the energy required to tunnel the holes already present in the valence band to the substrate 100 while preventing the formation of a new electron-hole pair.

Through the above-described process, tunneling of holes existing in the valence band of the semiconductor quantum dot 143 is promoted. Thus, holes are tunneled into the substrate 100 and the semiconductor quantum dots 143 remain electrically neutral. That is, the threshold voltage of the nonvolatile memory is higher than that of the write operation.

Through the above-described process, the nonvolatile memory device according to the present invention can perform a write operation and an erase operation by irradiating an optical signal. That is, data is recorded and erased only by the optical signal.

In addition, the nonvolatile memory device of the present invention can be used as an image sensor. That is, when the semiconductor quantum dot 143 is charged with a positive voltage according to the exposed time, and the source / drain is doped with n +, the threshold voltage of the field effect transistor is changed. This threshold voltage changes in correspondence with the time of exposure. For example, when the source / drain is doped with n +, the higher the exposure time or light intensity, the higher the voltage value of the semiconductor quantum dot is caused by the light passing through the transparent electrode layer, the threshold voltage of the transistor is reduced.

Thus, the exposed light can change the threshold voltage of the transistor to act as an image sensor.

In addition, the erasing operation of the image information recorded in the nonvolatile memory device tunnels holes present in the valence band of the semiconductor quantum dots to a substrate by applying an appropriate voltage to the transparent electrode layer 144 to reset the state of charge of the semiconductor quantum dots. It can be returned to the neutral state. The erase operation of the image may be performed through the above-described process.

4 is a graph illustrating capacitance-voltage characteristics of a nonvolatile memory device manufactured according to an exemplary embodiment of the present invention.

In FIG. 4, an n-type silicon substrate was used as the substrate, and the dielectric layer was made of silicon nitride. In addition, the thickness of silicon nitride was 150 nm. In addition, silicon quantum dots are used as quantum dots included in the dielectric layer, and indium oxide doped with gallium (Ga) is used as the transparent electrode layer, and the thickness is set to 200 nm.

Referring to FIG. 4, the capacitance-voltage characteristic curve is shifted in the negative voltage direction by the optical signal irradiated through the transparent electrode layer, and the movement of the capacitance-voltage characteristic curve in the negative voltage direction is It shows that the semiconductor quantum dots are positively charged. As the semiconductor quantum dots are positively charged, image information is written to the nonvolatile memory, and the threshold voltage of the field effect transistor is lowered.

Through the above-described process, the nonvolatile image memory device according to the present invention can perform a write operation of the frame memory by irradiation of an optical signal, and read and erase by applying an electrical signal.

1 is a cross-sectional view illustrating a nonvolatile memory device according to a preferred embodiment of the present invention.

FIG. 2 is an energy band diagram for describing a write operation of the nonvolatile memory device shown in FIG. 1.

FIG. 3 is an energy band diagram for explaining an erase operation of the nonvolatile memory device shown in FIG. 1.

4 is a graph illustrating capacitance-voltage characteristics of a nonvolatile memory device manufactured according to an exemplary embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

100: substrate 120: source / drain region

140: gate electrode 142: dielectric layer

143: semiconductor quantum dot 144: transparent electrode layer

Claims (12)

Board; Source / drain regions formed on the substrate; A gate electrode formed on the channel region between the source / drain regions; And the gate electrode changes a threshold voltage according to an irradiated optical signal. The method of claim 1, wherein the gate electrode, A dielectric layer formed over the channel region and having a semiconductor quantum dot; And And a conductive transparent electrode layer formed on the dielectric layer and transmitting an optical signal. 3. The dielectric layer of claim 2, wherein the dielectric layer is at least one selected from the group consisting of silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, aluminum nitride, magnesium oxide, hafnium oxide, silicon carbide, zinc oxide and gallium nitride. Or at least one selected from the group consisting of Alq3, P4MS, polyacryl, parylene, polymethylmethacrylate, polystyrene, PVP, and PET. The nonvolatile memory device of claim 2, wherein the semiconductor quantum dots are formed of Si, Ge, ZnO, GaN, CdSe, PbS, InP, CdS, ZnSe, or GaAs. The nonvolatile memory device of claim 2, wherein the transparent electrode layer is a TCO, a nitride compound, or a metal thin film. The method of claim 5, wherein the TCO is Ga-In-Sn-O, Zn-In-Sn-O, Ga-In-O, Zn-In-O, In-Sn-O, Zn-Sn-O, Mg -In-O, Ga-Zn-O or Al-Zn-O, the nitride compound is TiN or GaN, the metal thin film is Ni, Pt, Pb, Au, Ti, Al, In, Ca or a compound thereof Non-volatile memory device, characterized in that. 3. The method of claim 2, wherein the writing operation of the nonvolatile memory device supplies an optical signal having an energy of hv1 to the semiconductor quantum dots, so that the electrons are annealed in the generated electron-hole pairs, and holes are formed in the semiconductor quantum dots. A nonvolatile memory device characterized by remaining in the valence band. The non-volatile memory device of claim 7, wherein the erase operation of the nonvolatile memory device supplies an optical signal having an energy of hv2 to the semiconductor quantum dot to tunnel the hole remaining in the valence band of the semiconductor quantum dot. Memory element. The nonvolatile memory device of claim 7, wherein the erase operation of the nonvolatile memory device tunnels holes in the valence band of the semiconductor quantum dot to the substrate by applying a voltage to the semiconductor quantum dot. Board; Source / drain regions formed on the substrate; A gate electrode formed on the channel region between the source / drain regions; The gate electrode, A dielectric layer formed over the channel region and having a semiconductor quantum dot; And And a conductive transparent electrode layer formed on the dielectric layer and transmitting an optical signal, wherein a writing operation is performed as the optical signal is irradiated to the semiconductor quantum dots, and erased by applying an optical signal or a voltage to the semiconductor quantum dots. Nonvolatile memory device, characterized in that the operation is performed. The nonvolatile memory device of claim 10, wherein the energy of the optical signal irradiated to the semiconductor quantum dots during the write operation is equal to or more than an energy band gap of the semiconductor quantum dots. The nonvolatile memory device of claim 10, wherein the energy of the optical signal irradiated to the semiconductor quantum dot during the erase operation is equal to or less than an energy band gap of the semiconductor quantum dot.

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