CN101864592B

CN101864592B - Ferroelectric metal hetero-junction based memristor and preparation method thereof

Info

Publication number: CN101864592B
Application number: CN2010101724958A
Authority: CN
Inventors: 李海涛; 夏奕东; 徐波; 国洪轩; 殷江; 刘治国
Original assignee: Nanjing University
Current assignee: Nanjing University
Priority date: 2010-05-14
Filing date: 2010-05-14
Publication date: 2011-08-31
Anticipated expiration: 2030-05-14
Also published as: CN101864592A

Abstract

The invention relates to a ferroelectric metal hetero-junction based memristor; wherein the memristor material-ferroelectric lithium niobate is prepared by a pulse laser deposition system; monocrystal LN target material (4) is fixed on a target platform (5) of the pulse laser deposition system, and is placed in a growth chamber (6) of a pulse laser deposition film-making system; the vacuum in the growth chamber is pumped to be below 0.8*10-4Pa, oxygen gas flows in, and the oxygen pressure is from 25 to 35Pa, the substrate temperature is heated from 600-650 DEG; a KrF excimer laser is started, and the deposition time is determined according to monopulse energy; in-situ 500-650 DEG annealing is carried out 20-90min; the film has spontaneous polarization and 180-degree domain boundary; the memristor ferroelectric lithium niobate film is clamped between two metal electrode films to form a memristor unit with a miniature sandwich structure; the device can be applied to a high-density low-energy-consumption nonvolatile resistance random access memory.

Description

Based on memristor of ferroelectric metal hetero-junction and preparation method thereof

One, technical field

The invention belongs to the microelectronic material field, be specifically related to be applied to prepare the novel electron device---the ferroelectric material lithium niobate (LiNbO of memristor ₃, be called for short LN) and a kind of memristor element based on the ferroelectric metal hetero-junction structure.

Two, background technology

1971, Leon professor Chua of University of California Berkeley foretold theoretically, should have the 4th kind of circuit elements device except that resistance, electric capacity, inductance, and he is referred to as memristor, and has analyzed its feature that should have and function theoretically.The principal character of memristor is that it can realize memory function thus along with the variation that adds electric weight changes Resistance states.This electronic package provides possibility for the analog computer (analog computers) and the artificial neural network (artificial neuralnetworks) of the mode that realizes quicker more energy-conservation instant opening type PC (instant-on PCs) machine and picture human brain process information.

The theoretical model of memristor proposed after 37 years, the memristor antetype device that just has people such as the Strukov discovery of HP Lab to work.This antetype device unit is by two platinum electrodes and be clipped in TiO between two electrodes ₂Film constitutes.In order to realize adjusting, at TiO to the device resistance state ₂Introduce the oxygen room in the interface that film contacts with platinum, make metal and titanium dioxide upper and lower interface potential barrier asymmetric, the direction of the extra electric field by controlling parts and the migration that intensity is regulated oxygen room in the thin film of titanium oxide, thereby regulate the parameter that potential barrier is worn at the interface then, realize the purpose that the device resistance state is regulated along with extra electric field.

Memristor especially adopts the memristor circuit because its special electric property can bring the broad prospect of application that is difficult to predict, might realize the simulation to cerebral nerve cynapse mode of operation, for the realization of artificial neural network provides possibility.Yet except that the discovery of HP Lab, rarely has the memristor behavior of report other materials and structure.Therefore, press for the memristor material and the novel memristor device of design of the development of new of wider scope.

Three, summary of the invention

The objective of the invention is to: a kind of novel memristor material lithium niobate and a kind of memristor antetype device structure and preparation method thereof are provided.

Technical scheme of the present invention is: the ferroelectric lithium niobate of a kind of novel memristor material, and this film has spontaneous polarization and 180 ° of domain boundaries, and under External Electrical Field, the spontaneous polarization direction is overturn hardly; Adopt the LN ferroelectric thin film of the described high orientation of impulse laser deposition system (as shown in Figure 1) preparation, the process of its preparation is as follows:

A) monocrystalline LN target 4 is fixed on the target platform 5 of deposition film making system of pulse laser, substrate 1 is fixed on the substrate table 8, all is placed in the growth room 6 of deposition film making system of pulse laser;

B) with the interface valve 7 of vacuum pump by mechanical pump and molecular pump the vacuum in the growth room 6 is extracted into 0.8 * 10 ^-4Below the Pa, turn off molecular pump then, aerating oxygen from needle-valve 9 keeps in the growth room mobile oxygen voltage rise to being stabilized between 25～35Pa, and underlayer temperature is raised between 600～650 ℃;

C) start KrF excimer laser 2, laser beam is focused on the monocrystalline LN target 4 by condenser lens 3;

D) according to single pulse energy, determine sedimentation time, deposit thickness is the thick LN film of 50nm～100nm on substrate 1;

E) after thin film deposition finishes, 500～650 ℃ of annealing of original position, 20～90min.

The application of ferroelectric LN film in preparation memristor element:

Method and step that use LN ferroelectric thin film prepares the memristor element are as follows:

The memristor element be configured as sandwich structure (as shown in Figure 2) substantially, the LN film 12 that is about to crystallization is clipped in up and down and is built into a miniature sandwich structure between two metal electrodes 10,11, Here it is a memristor unit.The yardstick of effective perform region of LN film can be between 30nm to 200nm;

This sandwich structure prepares the silicon chip in silicon chip or thin layer of silicon dioxide covering, or on other backing material 13;

Above-mentioned electrode film 10,11 is platinum (Pt), or gold (Au);

The lead-in

wire

14,15 that upper/lower electrode 10,11 usefulness spun golds or copper wire are made is drawn, and so promptly constituting is a memristor unit.

The principle of work of the memristor that ferroelectric metal hetero-junction constitutes:

Memristor unit as shown in Figure 2:

1) add less voltage do the time spent (voltage＜1.0V) because the effect of catching/discharging electronics at LN/Pt (LN/Au) interface, formation discharges and recharges effect;

2) along with the increase of voltage strengthens, device presents the rectification feature, as shown in Figure 3, this be since the upper and lower interface that ferroelectric spontaneous polarization causes to wear barrier height then different, what the accumulation of the positive polarization charge at last interface made the interface wears the potential barrier reduction then;

3) along with the further increasing of scanning voltage (voltage＞2.5V), repeatably stable bipolarity resistive appears in device, as shown in Figure 4, the scanning voltage of forward makes component resistance reduce from high-impedance state, and the negative sense scanning voltage makes low resistance state be returned to original high-impedance state;

4) device is under the effect of forward voltage, and resistance state continues to change, and this promptly is that memristor is along with load " memory " Resistance states.(under 0 →+2.8 → 0V) scanning, the situation of change of its Resistance states as shown in Figure 5 at continuous forward voltage for the memristor components and parts.Wherein Fig. 5 (a) is, the IV curve under the effect of scan round voltage.As can be seen: in each circulation, electric current increases along with voltage refers to be index, for wearing electric current mechanism then; The electric current of voltage increase each time or decline process that is to say that all respectively greater than corresponding electric current in the last time circulation Resistance states that each circulation begins all is lower than last round-robin Resistance states; And when voltage got back to 0, electric current was also got back to 0 value, and this device noenergy accumulation is described.The voltage that the periodicity that Fig. 5 (b) opens for apportion loads, the electric current of periodic response and along with the variation of the resistance of the change of voltage cycle along with the time.As can be seen from the figure, Resistance states is periodically modulated along with adding three angle voltages.Red line is the nonlinear fitting to Resistance states after each loop ends among the figure, and as can be seen, Resistance states is along with time index is decayed.

The performance test of the memristor that is made of ferroelectric metal hetero-junction: the key instrument that the memristor element is carried out performance test is Keithley 2400 source measurement units, mainly tests the response of antetype device to varying voltage signal.

Beneficial effect of the present invention is: the memristor antetype device that the present invention proposes first based on ferroelectric metal hetero-junction, and use this ferroelectric metal hetero-junction memristor element to have following beneficial effect:

A) under positive and negative cyclical voltage effect, device can be stablized conversion between high low resistance state, makes this device might be applied to the Nonvolatile resistance variation memory of following high density low energy consumption;

B) under the forward voltage effect that continues, resistance state periodically diminishes, and is used for storage, can realize being different from two kinds of attitudes of 1 and 0, but almost unlimited many states, its configuration all is non-volatile, this provides possibility for realizing application such as novel analog formula computing machine.

C) the memristor storage signal is relevant with the outside signal histories that is loaded, and utilization is recalled resistance circuit and carried out the signal transmission, can realize being similar to the function that the nervous system signal transmits cynapse, for realizing that artificial neural network provides possibility.

Four, description of drawings

Fig. 1: the structural representation of the pld (pulsed laser deposition) growing system of preparation LN film,

The 1-backing material; The 2-KrF excimer laser; The 3-condenser lens; 4-LN monocrystalline target; 5-target platform; The 6-growth room; The interface valve of 7-mechanical pump and molecular pump; The 8-substrate table; In the growth room, the ventilate gas admittance valve of body of 9-.

Fig. 2: based on the memristor cellular construction synoptic diagram of ferroelectric metal hetero-junction,

The 10-Pt top electrode; The 11-Pt bottom electrode; The LN film of 12-crystallization; The 13-silicon substrate; 14-top electrode lead-in wire; 15-bottom electrode lead-in wire.

Fig. 3: the rectification characteristic test result figure of memristor unit, wherein transverse axis is represented the suffered voltage of device, the longitudinal axis is represented the response current of device, the process that voltage applies is from 0V, to+1.6V, to 0V, arrive again-1.6V, get back to 0V at last, voltage signal is the step pattern, and the time width of step is about 100ms.

Fig. 4: the bipolarity resistive test result figure of memristor unit, the process that voltage applies is from 0V, to+2.8V, to 0V, arrive again-2.8V, get back to 0V at last.

Fig. 5: the resistance state of memristor unit changes test result figure continuously, the process that voltage applies is from 0V, to+2.8V, arrive 0V again, so repeated for five each and every one, wherein figure (a) is for repeating the current-voltage characteristic in five cycles in cycles, the voltage of the periodicity loading that figure (b) opens for apportion, the electric current of periodic response and along with the resistance of the change of voltage cycle, and to the configuration nonlinear fitting result of exponential damping in time.

Five, embodiment

Embodiment 1: the preparation method of ferroelectric phase lithium niobate, and its preparation process is as follows:

A) monocrystalline LN target 4 is fixed on the target platform 5 of deposition film making system of pulse laser, substrate 1 is fixed on the substrate table 8, all be placed in the growth room 6 of deposition film making system of pulse laser;

B) with the interface valve 7 of vacuum pump by mechanical pump and molecular pump growth room 6 is evacuated down to 0.8 * 10 ^-4Below the Pa, the closure molecule pump;

C) regulate gas admittance valve 9, making the mobile oxygen pressure in the growth room is 25～35Pa;

D) use resistance-heated furnace heated substrate platform 5, make the temperature of substrate 4 rise to 600～650 ℃;

E) rotation substrate table 5 and target platform 8;

F) start KrF excimer laser 2, wavelength 248nm, pulse width 30ns, frequency 5Hz, single pulse energy 400mJ focuses on the monocrystalline LN target 4 laser beam scioptics 3;

G) deposition 15～40min, deposition LN film on substrate 4.

H) after thin film deposition finishes, 500～650 ℃ of annealing 20～90min.

Embodiment 2. is based on the preparation method of the sandwich structure memristor unit of ferroelectric metal knot, and concrete preparation process is as follows:

A) at Pt/Ti/SiO ₂On/Si (111) substrate, be about the LN film of 50nm～100nm with PLD method growth thickness, and live one jiao of substrate with the compressing tablet cramping in deposition process, the part Pt film that spills like this will be as bottom electrode;

B) the LN film of taking-up crystallization from the PLD growth room covers mask plate, and with magnetron sputtering or other film plating process, the Pt thickness of electrode so just constitutes a miniature sandwich structure at 100nm～150nm in the growth; If Au/Ti/SiO ₂/ Si (111) substrate, growth top electrode Au obtains essentially identical result;

C) pick out copper lead-in

wire

14,15 by upper/lower electrode film 10,11 respectively at last, this just constitutes a memristor unit.

Claims

1. A memristor material ferroelectric lithium niobate is characterized in that it is prepared by a pulsed laser deposition system: the single crystal LN target (4) is fixed on the target table (5) of the pulsed laser deposition film-making system, and the lining The bottom (1) is fixed on the substrate table (8), and both the target table (5) and the substrate table (8) are placed in the growth chamber (6) of the pulsed laser deposition film-making system; Vacuum down to below 0.8×10 ^-4 Pa, and feed oxygen, keep the flow oxygen pressure in the growth chamber up to 25-35Pa and maintain it, and raise the substrate temperature to 600-650°C; start the KrF excimer laser ( 2), focus the laser beam on the single crystal LN target (4) through the focusing lens (3); determine the deposition time according to the energy of the single pulse, and deposit an LN film with a thickness of 30nm to 200nm on the substrate (1) ; After the film deposition, in-situ annealing at 500-650° C. for 20-90 minutes; the film has spontaneous polarization and 180° domain boundaries.

2. The application of the memristor material ferroelectric lithium niobate according to claim 1 in the preparation of memristor elements: it is characterized in that the basic configuration of the memristor element is a sandwich structure, and the memristor material ferroelectric niobium Lithium oxide film (12) is sandwiched between the upper and lower metal electrode films (10, 11) to form a micro-sandwich structure, which is a memristor unit, and the ferroelectric lithium niobate film is between 30nm and 200nm; the sandwich The structure is prepared on a silicon wafer or a silicon wafer covered with a thin layer of silicon dioxide, and the metal electrode film is platinum or gold.

3. The application of the memristor material ferroelectric lithium niobate according to claim 2 in the preparation of memristor elements: it is characterized in that the thickness of the memristor material ferroelectric lithium niobate film is 50nm～100nm, and the thickness of the upper and lower electrodes 100nm to 150nm.