Lamination design-based hafnium-zirconium-ferroelectric device and preparation method thereof

Abstract

The invention provides a hafnium-zirconium-ferroelectric device based on lamination design and a preparation method of the hafnium-zirconium-ferroelectric device. According to the hafnium zirconium ferroelectric device, a lanthanum strontium manganese oxide bottom electrode layer, a ferroelectric functional layer and a top electrode layer are sequentially formed on a strontium titanate substrate, wherein the ferroelectric functional layer is of a laminated structure formed by alternately arranging HfO2 and ZrO2. The preparation method of the hafnium-zirconium-ferroelectric device comprises the following steps: pretreating a substrate, firstly sputtering a lanthanum strontium manganese oxide target material on a strontium titanate substrate by adopting a pulse laser deposition process to form a lanthanum strontium manganese oxide bottom electrode layer, and then sequentially sputtering zirconium oxide and a hafnium oxide target material on the lanthanum strontium manganese oxide bottom electrode layer by adopting the pulse laser deposition process to form the hafnium-zirconium-ferroelectric device. And a laminated structure in which zirconium oxide and hafnium oxide alternately grow is formed. The laminated ferroelectric device prepared by the invention presents a relatively stable storage state, and is relatively small in current order of magnitude, lower in switching voltage, low in power consumption and wide in application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of ferroelectric devices, and specifically to a hafnium zirconium ferroelectric device based on a stacked design and a preparation method thereof. Background Art

[0002] Since the breakthrough of the stacked ferroelectric memristor based on hafnium oxide (HfO2) in 2016, the optimization of ferroelectric properties has become the focus. At present, the traditional methods for improving its ferroelectric properties (such as element doping, changing the type of top electrode, and changing process parameters) have limitations. The stacked structure design of HfO2 and ZrO2 provides a new idea for improving ferroelectricity. Their phase structures are similar, the preparation technologies overlap and are compatible with the CMOS process. The stack forms a quasi-superlattice structure, which can suppress the non-ferroelectric M phase and promote the stability of the O phase, improve the polarization intensity and the remanent polarization value, and also solve the problem of performance degradation of ultrathin ferroelectric films. The team of Tsinghua University used atomic layer deposition technology to construct a periodic stacked structure to achieve the collaborative regulation of ferroelectric phase and interface engineering, and improve the proportion of ferroelectric orthorhombic phase and suppress the non-ferroelectric monoclinic phase. In 2018, IMEC reduced the stacked thickness to 5 nm, stabilized the vertical orientation of ferroelectric domains, and refreshed the reliability record. The hafnium zirconium stacked system realizes the controllable movement of ferroelectric domain walls through gradient oxygen vacancy engineering. The ZrO2 layer pins the migration of oxygen vacancies, reduces the polarization switching voltage, and the stacked structure suppresses the generation of phase boundary defects and maintains a high polarization value.

[0003] In recent years, with the rapid development of digital communication, big data, and Internet of Things technologies, the demand for high-density, low-power, and high-speed non-volatile memories has become increasingly urgent. The current integrated circuit process has entered the node below 20 nm, and traditional non-volatile memories (such as Flash) face severe challenges due to physical limits, and a new generation of storage technology breakthroughs are urgently needed. Summary of the Invention

[0004] The purpose of the present invention is to provide a hafnium zirconium stacked ferroelectric device and a preparation method thereof, so as to provide a new high-performance non-volatile ferroelectric storage device with stable storage, good anti-fatigue durability, and fast operation speeds such as reading, writing, and erasing.

[0005] The present invention is implemented as follows: A hafnium zirconium ferroelectric device based on a stacked design is provided, specifically, a lanthanum strontium manganese oxide bottom electrode layer, a ferroelectric functional layer, and a top electrode layer are sequentially formed on a strontium titanate substrate, and the ferroelectric functional layer is a stacked structure in which HfO2 and ZrO2 are alternately arranged.

[0006] Further, the thickness of the lanthanum strontium manganese oxide bottom electrode layer is 46 nm.

[0007] Further, the ferroelectric functional layer is a four-layer structure, which is ZrO2-HfO2-ZrO2-HfO2 from bottom to top in sequence, and the thickness of each layer of HfO2 and each layer of ZrO2 is 6 nm.

[0008] The present invention also provides a method for preparing a hafnium-zirconium ferroelectric device based on a stacked design, comprising the following steps:

[0009] (1) Pretreat the strontium titanate substrate;

[0010] (2) Stick the strontium titanate substrate on a tray and place it into a pulsed laser deposition system;

[0011] (3) Place lanthanum strontium manganite, zirconium oxide, and hafnium oxide targets into the pulsed laser deposition system;

[0012] (4) First, use the pulsed laser deposition process to sputter the lanthanum strontium manganite target on the strontium titanate substrate to form a lanthanum strontium manganite bottom electrode layer;

[0013] (5) Then, use the pulsed laser deposition process to sequentially sputter the zirconium oxide and hafnium oxide targets on the lanthanum strontium manganite bottom electrode layer to form a stacked structure with alternating growth of zirconium oxide and hafnium oxide;

[0014] (6) Finally, use the magnetron sputtering process to deposit a top electrode layer on the stacked structure with alternating growth of zirconium oxide and hafnium oxide.

[0015] Further, in step (1), the pretreatment of the strontium titanate substrate is specifically: first, ultrasonically clean the strontium titanate substrate with acetone, secondly, ultrasonically clean it with alcohol, and finally dry it with nitrogen.

[0016] Further, in step (4), first, heat the tray to 750 °C, then pre-sputter the lanthanum strontium manganite target for 1000 pulse numbers, and then officially sputter the lanthanum strontium manganite target for 9000 pulse numbers.

[0017] Further, in step (4), heating the tray to 750 °C specifically means: heating it to 600 °C at a heating rate of 25 °C / min, and then heating it to 750 °C at a heating rate of 20 °C / min.

[0018] Further, in step (5), heat the tray to 900 °C, then pre-sputter the zirconium oxide target for 1000 pulse numbers, then officially sputter the zirconium oxide target for 1500 pulse numbers; then pre-sputter the hafnium oxide target for 1000 pulse numbers, and then officially sputter the hafnium oxide target for 1500 pulse numbers; then officially sputter the zirconium oxide target for 1500 pulse numbers again, and finally officially sputter the hafnium oxide target for 1500 pulse numbers to obtain a four-layer thin film structure of zirconium oxide - hafnium oxide - zirconium oxide - hafnium oxide.

[0019] Further, in step (5), heat the tray to 900 °C at a heating rate of 10 °C / min.

[0020] Further, in step (4), the growth pressure of the lanthanum strontium manganite bottom electrode layer is 195.5 mTorr, and in step (5), the growth pressure of the stacked structure with alternating growth of zirconium oxide and hafnium oxide is 97.5 mTorr.

[0021] The present invention has the following beneficial effects:

[0022] 1. The hafnium-zirconium ferroelectric device based on the stacked design and its preparation method provided by the present invention can effectively solve the problem that the ferroelectric performance of existing hafnium oxide ferroelectric devices is prone to instability due to polycrystallization. The preparation method uses pulsed laser molecular beam epitaxy technology (Laser-MBE) to construct a periodic HfO2-ZrO2 stack layer by layer (the number of periods is 2-4), and a complete electrical device structure is prepared through a magnetron sputtering system.

[0023] 2. The present invention solves the problem of the sharp degradation of the performance of ultra-thin ferroelectric films through atomic-level heterostructure engineering. This structure can achieve better electrical repeatability, lower operating voltage (1.3V ± 0.3V), and higher remanent polarization intensity.

[0024] 3. The preparation method provided by the present invention is environmentally friendly and simple to implement. The prepared ferroelectric device has good ferroelectric performance through performance testing, shows a relatively stable storage state, and its electrical testing shows a smaller current order of magnitude and a lower switching voltage, enabling low power consumption of the device. The stacked device has good performance and is a ferroelectric device with more stable storage performance, strong durability, and broader application prospects. Description of the Drawings

[0025] Figure 1 is a schematic structural diagram of the hafnium-zirconium ferroelectric device provided by the present invention.

[0026] Figure 2 is a schematic structural diagram of the four-layer hafnium-zirconium ferroelectric device prepared in Example 1.

[0027] Figure 3 is a schematic structural diagram of the two-layer hafnium-zirconium ferroelectric device prepared in the comparative example

[0028] Figure 4 is a TEM image of the functional layer of the two-layer hafnium-zirconium ferroelectric device prepared in the comparative example.

[0029] Figure 5 is an XRD test result diagram of the hafnium-zirconium ferroelectric devices prepared in Example 1 and the comparative example.

[0030] Figure 6 is a ferroelectric remanent polarization test result diagram of the hafnium-zirconium ferroelectric devices prepared in Example 1 and the comparative example.

[0031] Figure 7It is the I-V test result diagram of the hafnium-zirconium ferroelectric devices prepared in Example 1 and the comparative example; among them, the left figure corresponds to the two-layer hafnium-zirconium ferroelectric device, and the right figure corresponds to the four-layer hafnium-zirconium ferroelectric device.

[0032] Figure 8 It is the statistical chart of the operable voltage of the four-layer hafnium-zirconium ferroelectric device prepared in Example 1. Detailed implementation manners

[0033] The present invention will be further described below in combination with the comparative example and the example. The following implementation manners are only for illustration and do not limit the protection scope of the present invention in any form.

[0034] The method for hafnium-zirconium ferroelectric devices based on a stacked design provided by the present invention uses strontium titanate SrTiO3 (abbreviated as STO, crystal orientation is 001) as a substrate. Lanthanum strontium manganite La 0.67 Sr 0.33 MnO3 (abbreviated as LSMO) as the bottom electrode. By changing the different growth designs of hafnium oxide (HfO2) and zirconium oxide (ZrO2), the crystallization quality of the ferroelectric orthorhombic phase of the hafnium-zirconium stacked ferroelectric thin film can be significantly improved, and its ferroelectric properties can be significantly improved. And the electrical tests of its ferroelectric devices are significantly improved. The structure of the hafnium-zirconium ferroelectric device is as Figure 1 shown.

[0035] Example 1

[0036] The present invention uses pulsed laser molecular beam epitaxy technology to prepare ferroelectric devices of LSMO, HfO2, and ZrO2. The preparation steps are as follows:

[0037] (1) First, the single-crystal strontium titanate (STO) substrate is first placed in an acetone solution and ultrasonically cleaned for 10 minutes to remove the stains on its surface, and then placed in an alcohol solution and ultrasonically cleaned for 10 minutes to wash off the acetone solvent remaining on it. After taking it out, it is dried with high-purity nitrogen and reserved.

[0038] (2) Use quick-drying silver glue to stick the STO substrate on the heater tray to prepare for the experiment.

[0039] (3) Place the heater tray with the STO substrate adhered onto it into the vacuum chamber. Open the gas inlet command of the loadlock (sample introduction chamber) in the pulsed molecular beam epitaxy system and wait for the loadlock to be filled with nitrogen until it automatically opens at atmospheric pressure. Place the tray into the loadlock and close the chamber door of the loadlock. Turn on the mechanical pump and molecular pump of the loadlock for initial vacuum treatment. After waiting for the pressure in the loadlock to drop below 37.5 mTorr, the system will automatically turn on the molecular pump for high vacuum treatment. After waiting for the pressure in the loadlock to drop to 1E-7 Torr, open the gate valve between the loadlock chamber and the main chamber (growth chamber / main chamber), push the heating tray into the fixed position in the main chamber and then pull it out, and close the gate valve. Send the LSMO, HfO2, and ZrO2 targets into the main chamber using the same steps to complete the feeding of the targets and prepare for the formal temperature increase experiment.

[0040] (4) Lower the external heating jacket before the formal temperature increase to make it fit the heater tray. Turn on the heating module of the system, control the heating rate before 600 °C at 25 °C / min, and control the heating rate after 600 °C at 20 °C / min until the temperature rises to 750 °C. Wait for 5 min for the temperature to stabilize, then introduce oxygen and turn on the excimer pulsed laser for preheating. Close the sample baffle and adjust the optical path of the laser to ensure that the laser accurately irradiates the corresponding LMSO target. After the laser is charged, pre-sputter the LSMO target to be deposited to remove surface impurities. The laser used is a KrF excimer laser with a wavelength of 248 nm (λ = 248 nm), and the laser energy density is controlled at 1.25 J / cm 2 , and the frequency is 5 Hz. To remove the surface contaminants of the target, perform 1000 pulse numbers of pre-sputtering. The growth pressure of LSMO is 195.5 mTorr, and the system cooperatively adjusts the angle of the gate valve and the oxygen flow rate (automatically controlled by the system, only the target pressure needs to be input). After the pre-sputtering is completed, open the tray baffle and start growing the LSMO bottom electrode on the STO substrate formally. Set the number of pulses to 9000 and start formal sputtering. After the sputtering is completed, keep the system settings unchanged and wait for 5 min.

[0041] (5) Start depositing hafnium oxide and zirconium oxide at this time. Set the heating rate to 10 °C / min and raise the temperature to 900 °C. Input the target pressure of 97.5 mTorr and wait for 5 min for the pressure and temperature to stabilize. Before formally depositing the hafnium oxide and zirconium oxide films, first perform 1000 pulse numbers of pre-deposition, and then deposit formally. First deposit zirconium oxide, set 1500 pulse numbers, and then deposit hafnium oxide and set 1500 pulse numbers. This process is repeated once to ensure that the total number of pulse numbers remains 6000, and a four-layer film of ZrO2 - HfO2 - ZrO2 - HfO2 is obtained.

[0042] (6) To fabricate a complete electrical device, the growth of the top electrode is also required after the thin film deposition is completed. After waiting for the temperature of the pulsed laser molecular beam epitaxy system to drop, the sample is taken out onto the transfer rod again, and then taken out into the loadlock chamber. The loadlock chamber is automatically filled with gas to atmospheric pressure and opened, and the sample is taken out and placed on the sample stage in the magnetron sputtering vacuum chamber. A mask plate is placed on the substrate where the ferroelectric functional layer is formed, and the mask plate is evenly distributed with circular holes with a diameter of 50 μm. The chamber is evacuated to 1.8×10 -4 Pa, argon gas with a flow rate of 25 sccm is introduced into the chamber, the interface valve is adjusted to maintain the pressure in the chamber at 1 Pa, the AC source for controlling the target ignition is turned on, the power of the AC source is adjusted to 10 W to ignite the target, and pre-sputtering is carried out for 4 - 6 min; then formal sputtering is carried out to form a Pd top electrode on the ferroelectric functional layer. The sputtering time of the Pd top electrode is about 12 min, and the thickness is 20 nm.

[0043] The structure of the four-layer hafnium zirconium ferroelectric device prepared in this embodiment is as Figure 2 shown.

[0044] Comparative example

[0045] The device fabrication method is the same as that of Example 1. When growing the thin film structure in step (5), hafnium oxide is deposited first, and 3000 pulse numbers are set. Then the target is changed, and zirconium oxide is deposited, and 3000 pulse numbers are set. At this time, the structure is a two-layer thin film of ZrO2 - HfO2.

[0046] The structure of the two-layer hafnium zirconium ferroelectric device prepared in the comparative example is as Figure 3 shown.

[0047] Performance test:

[0048] The two-layer ferroelectric device prepared in the comparative example is subjected to TEM test, and the results are as Figure 4 shown. The figure shows that a 46-nm-thick LSMO thin film is grown on the STO substrate, followed by ZrO2 thin film and HfO2 thin film with a thickness of 6 nm each

[0049] The four-layer hafnium zirconium ferroelectric device prepared in Example 1 and the two-layer hafnium zirconium ferroelectric device prepared in the comparative example are subjected to XRD test, and the results are as Figure 5 shown. It can be found that the full width at half maximum of the ferroelectric orthorhombic phase of the four-layer device at 30° is larger than that of the two-layer device, which highlights the better performance of the four-layer stacked hafnium zirconium device.

[0050] The four-layer hafnium zirconium ferroelectric device prepared in Example 1 and the two-layer hafnium zirconium ferroelectric device prepared in the comparative example are subjected to ferroelectric performance test, and the results are as Figure 6 shown. It can be found that the ferroelectric performance of the device has been significantly improved, from 2 μC / cm² of the two-layer device2 Increased to 10 μC / cm for four layers 2 .

[0051] The I-V curve tests were performed on the four-layer hafnium zirconium ferroelectric device prepared in Example 1 and the two-layer hafnium zirconium ferroelectric device sample prepared in the comparative example. The results are as Figure 7 shown, demonstrating the electrical characteristics exhibited by the four-layer and two-layer ferroelectric devices. It can be concluded that the four-layer ferroelectric device has better stability and a larger bipolar resistive switching window.

[0052] The switching voltage test was performed on the four-layer hafnium zirconium ferroelectric device sample prepared in Example 1. The results are as Figure 8 shown. The four-layer device has a lower switching operation voltage (1.3 V ± 0.3 V), indicating that the device has lower power consumption.

[0053] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the described embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A hafnium-zirconium ferroelectric device based on a stacked design, characterized in that: A lanthanum strontium manganese oxide bottom electrode layer, a ferroelectric functional layer and a top electrode layer are sequentially formed on a strontium titanate substrate. The ferroelectric functional layer is a stacked structure in which HfO2 and ZrO2 are alternately arranged.

2. The hafnium zirconium ferroelectric device based on a stacked design according to claim 1, characterized in that: The thickness of the lanthanum strontium manganese oxide bottom electrode layer is 46 nm.

3. The hafnium zirconium ferroelectric device based on a stacked design according to claim 1, characterized in that: The ferroelectric functional layer has a four-layer structure, which is ZrO2-HfO2-ZrO2-HfO2 from bottom to top, and the thickness of each HfO2 layer and each ZrO2 layer is 6nm.

4. A method for preparing a hafnium-zirconium ferroelectric device based on a stacked design, characterized in that: The following steps are involved: (1) pretreating a strontium titanate substrate; (2) sticking the strontium titanate substrate on a tray and placing it in a pulsed laser deposition system; (3) placing lanthanum strontium manganese oxide, zirconium oxide, and hafnium oxide targets into a pulsed laser deposition system; (4) firstly sputtering a lanthanum strontium manganese oxide target on a strontium titanate substrate by a pulsed laser deposition process to form a lanthanum strontium manganese oxide bottom electrode layer; (5) subsequently sputtering zirconium oxide and hafnium oxide targets on the lanthanum strontium manganese oxide bottom electrode layer in sequence by a pulsed laser deposition process to form a stacked structure in which zirconium oxide and hafnium oxide grow alternately; (6) Finally, a top electrode layer is deposited on the alternately grown stacked structure of zirconium oxide and hafnium oxide using a magnetron sputtering process.

5. The method for preparing a hafnium-zirconium ferroelectric device based on a stacked design according to claim 4, characterized in that: Step (1) pre-treats the strontium titanate substrate, specifically: firstly, ultrasonically cleans the strontium titanate substrate with acetone, then ultrasonically cleans it with alcohol, and finally blows it dry with nitrogen.

6. The method for preparing a hafnium-zirconium ferroelectric device based on a stacked design according to claim 4, characterized in that: In step (4), the tray is first heated to 750° C., and then the lanthanum strontium manganese oxide target is pre-sputtered for 1000 pulses, followed by the formal sputtering of the lanthanum strontium manganese oxide target for 9000 pulses.

7. The method for preparing a hafnium-zirconium ferroelectric device based on a stacked design according to claim 6, characterized in that: In step (4), the tray is heated to 750°C by heating to 600°C at a heating rate of 25°C / min, and then heating to 750°C at a heating rate of 20°C / min.

8. The method for preparing a hafnium-zirconium ferroelectric device based on a stacked design according to claim 4, characterized in that: In step (5), the tray is heated to 900° C., and then the zirconium oxide target is pre-sputtered for 1000 pulses, and then the zirconium oxide target is formally sputtered for 1500 pulses; then the hafnium oxide target is pre-sputtered for 1000 pulses, and then the hafnium oxide target is formally sputtered for 1500 pulses; After that, the zirconium oxide target is formally sputtered for 1500 pulses, and finally the hafnium oxide target is formally sputtered for 1500 pulses to obtain a four-layer thin film structure of zirconium oxide-hafnium oxide-zirconium oxide-hafnium oxide.

9. The method for preparing a hafnium-zirconium ferroelectric device based on a stacked design according to claim 9, characterized in that: In step (5), the tray is heated to 900° C. at a heating rate of 10° C. / min.

10. The method for preparing a hafnium-zirconium ferroelectric device based on a stacked design according to claim 4, characterized in that: The growth pressure of the lanthanum strontium manganese oxide bottom electrode layer in step (4) is 195.5 mTorr, and the growth pressure of the stacked structure of alternating growth of zirconium oxide and hafnium oxide in step (5) is 97.5 mTorr.

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