A nano-neuromorphic device with an organic two-dimensional conjugated symmetric polymer as an active layer, and a preparation method and application thereof

Abstract

The application belongs to the field of organic / polymer neuromorphic devices, and specifically provides a nano neuromorphic device with an organic two-dimensional conjugate symmetric polymer as an active layer, and a preparation method and application thereof. The nano device is manufactured in the form of an 8*8 cross switch array through electron beam lithography technology and stripping method, and the width of the word line and the bit line is 100 nm and 200 nm respectively, which is a very small nano structure. The device realizes record-high yield of the polymer memristor with minimization and low potential, and simultaneously realizes fast response within 20-40 ns, the variation range of D2D is less than 10%, the device yield is higher than 90%, and the device can reach 50-100 nm scale, and the power consumption is lower than 20 J / bit. The polymer memristor array can realize storage and calculation integration, and can be used for information storage, and has excellent application prospect in the field of artificial intelligence.

Description

A nano-neuromorphic device with an organic two-dimensional conjugated symmetry polymer as the active layer, its preparation method and application Technical Field

[0001] This invention belongs to the field of organic / polymer neuromorphic information storage technology, specifically providing a method for preparing and applying a lightweight polymer nano-neuromorphic device with good mechanical flexibility. Specifically, it relates to a DA-type two-dimensional-conjugated symmetric polymer as the active layer of an organic nanoscale neuromorphic device, its preparation method, testing method, and application in the field of low-power information storage. Background Technology

[0002] In today's era of the Internet of Things, big data, and artificial intelligence, global data is exponentially exploding in numerous fields such as municipal traffic control, domestic security monitoring, pharmaceutical services, and industrial production, reaching 40 trillion gigabytes, or 5 megabytes per person by 2020. Large amounts of analog signals from sensor terminals are typically uploaded to the cloud via remote data centers and shared computing resources for massive storage and on-demand processing. Therefore, energy shortages may be the most severe challenge facing the information technology industry by the middle of this century. However, the structural inhomogeneity of most resistive switching media often leads to random and highly localized resistive switching characteristics, thus reducing the yield and reliability of nanoscale memristors in practical applications. Therefore, designing and fabricating novel memristor materials and developing memristors with excellent retention, durability, and device-to-device (D2D) performance consistency are urgent desires and formidable challenges in extending Moore's Law lifetime and overcoming the von Neumann communication bottleneck. Two-dimensional conjugated polymers are among the most promising materials today, attracting widespread attention from researchers due to their high conjugation, unique planarity, ultra-high surface area, tunable pore size, and ease of functionalization. Recent thorough research has revealed a neuromorphic memristor based on two-dimensional conjugated organic polymers that exhibits excellent characteristics such as CMOS compatibility, fast switching speed, and low power consumption, thus being considered a candidate for a new generation of high-density information storage. Currently, while existing technologies utilize two-dimensional materials as the active layer, most involve grafting polymers onto two-dimensional materials to create common sandwich-structure devices, which cannot achieve nanoscale dimensions and may still not meet Moore's Law requirements. However, there are few reports of fabricating extremely small nanoscale devices using pure polymers as the active layer and employing photolithography and lift-off techniques. Summary of the Invention

[0003] The purpose of this invention is to propose a neuromorphic device fabricated in the form of an 8×8 cross-switch array using electron beam lithography and a lift-off method, with word lines and bit lines having extremely small nanoscale structures of 100 nm and 200 nm widths, respectively.

[0004] The second objective of this invention is to propose a lightweight, mechanically flexible nanoneuromorphic device based on a polymer with a DA-type two-dimensional conjugated structure and excellent symmetry.

[0005] The third objective of this invention is to provide a method for preparing a lightweight polymer nano-neuromorphic device with good mechanical flexibility, using a DA-type two-dimensional conjugated polymer film as the active layer.

[0006] The fourth objective of this invention is to provide a testing method for nanoscale neuromorphic devices using organic two-dimensional conjugated symmetric polymers as the active layer.

[0007] The fifth objective of this invention is to provide an application of an organic nano-neuromorphic device with an organic two-dimensional conjugated symmetric polymer as the active layer in the field of low-power information storage.

[0008] The technical solution of this invention:

[0009] A nano-neuromyctic device using an organic two-dimensional conjugated symmetric polymer as the active layer is described. It has a sandwich structure formed by forked electrodes, consisting of a transverse electrode layer, a middle active layer of a polymer PBDT-BDQTPA film, and a vertical electrode layer. The structure of the polymer PBDT-BDQTPA film is shown in the following formula:

[0010]

[0011] n takes values ​​≥ 20

[0012]

[0013] This invention provides an organic nano-neuromorphic device using a novel DA-type two-dimensional-conjugated symmetric polymer thin film material as the active layer. The conductivity of the PBDT-BDQTPA thin film in this device is uniform at the submicron scale, with a distance of approximately 40 nm between adjacent switching points. This indicates that the scaling limit of the polymer memristor of this invention can be extended to the 100 nm range, with a theoretical power consumption of approximately 10–20 J / bit. Such a small device is fabricated using electron beam lithography and a lift-off method in the form of an 8×8 cross-switch array, with word line and bit line widths of 100 nm and 200 nm, respectively, representing an extremely small nanoscale structure.

[0014] Further optimization shows that the device exhibits significantly different resistance states under different voltages. These states are defined as "on" and "off" and can be used as "0" and "1" in binary to store data, and the data can still be preserved after power is turned off.

[0015] Further optimization resulted in the device being fabricated in the form of an 8×8 cross switch array using electron beam lithography and a stripping method.

[0016] This invention also provides a method for preparing a lightweight polymer nano-neuromorphic device with good mechanical flexibility using a DA-type two-dimensional conjugated symmetry polymer film as the active layer, comprising the following steps:

[0017] (1) Forming longitudinal and transverse electrode strips with a width of 50-100 nm and a spacing of 150-200 nm on a SiO2 / Si substrate;

[0018] (2) By using Vistec EBPG-5200 + Electron beam lithography of the electron beam lithography system and electron beam evaporation of the 15-20nm Au layer on top of the 5-10nm Ti adhesion layer on the Denton electron beam evaporator are used to pattern the bottom electrode strips.

[0019] (3) After lifting, spin-coat 50-80 μL of PBDT-BDQTPA toluene solution (5 mg / mL) onto the Siwafer at a speed of 1000-3000 rpm for 50-100 s, and then dry it thoroughly in a vacuum at 50-100 °C overnight.

[0020] (4) Finally, electron beam lithography, electron beam evaporation and stripping are used similarly to pattern and deposit a top electrode consisting of 10-15 nm Ti and 40-50 nm Au, thereby completing the fabrication of the device and finally obtaining the device PBDT-BDQTPA.

[0021] This invention also provides a testing method for organic nano-neuromorphic devices using a two-dimensional organic conjugated symmetry polymer as the active layer, comprising the following steps:

[0022] 1) All electrical measurements used to fabricate the device in this work were performed on a Keithley 4200 semiconductor parameter analyzer equipped with a pulse measurement unit, thus providing further protection for the device under these environmental conditions; 2) In C-AFM measurements, a PBDT-BDQTPA film was spin-coated onto a glass substrate coated with ITO.

[0023] 3) Finally, the bias voltage is applied directly to the polymer film by using the Pt-coated C-AFM tip as a movable top electrode to complete the morphology test of the device.

[0024] The structure of the polymer PBDT-BDQTPA in the active layer film provided by this invention is shown in the following formula: n ranges from ≥20.

[0025]

[0026] The present invention also provides an application of the organic nano-neuromorphic device with conjugated polymer as active layer in the field of low-power information storage.

[0027] Furthermore, the device exhibits distinctly different resistance states under different voltages. These states can be defined as "on" and "off" and can be used as "0" and "1" in binary to store data, and the data can still be preserved after power is turned off.

[0028] Furthermore, this application is the use of an organic two-dimensional conjugated symmetry polymer memory with an ultra-low threshold voltage in a low-power nanoscale neuromorphic device.

[0029] This invention proposes using pure two-dimensional-conjugated polymer materials as the active layer of neuromorphic devices, and designs and synthesizes a DA-type two-dimensional-conjugated polymer. This invention selects benzodithiophene (BDT) and quinoxaline units with suitable electron-withdrawing capabilities as the polymer backbone, and modifies the BDT side chains with thiophene derivatives to enable the formation of a two-dimensional-conjugated structure. Furthermore, it selects to covalently graft symmetrical triphenylamine groups around the thiophene, thereby forming a polymer PBDT-BDQTPA (polybenzodithiophene-quinoxaline).

[0030] The active layer of the device described in this invention is a thin film of a novel polymer material, PBDT-BDQTPA, with side chains that can be substituted with different long alkyl chains. By using a symmetrical derivative of a two-dimensional conjugated polymer as the active layer, coplanar macromolecules are constructed to enhance the π-π stacking and crystallinity of the film, thereby achieving homogeneous transformation throughout the polymer layer. This device achieves record-breaking high yield of polymer memristors with minimal power consumption and low potential, while exhibiting a fast response within 20–40 ns, a D2D variation of less than 10%, a device yield of over 90%, and can reach a scale of 50–100 nm with power consumption below 20 J / bit. This polymer memristor array enables in-memory computing and can be used for information storage, showing excellent application prospects in the field of artificial intelligence.

[0031] This invention relates to a neuromorphic device based on Au / PBDT-BDQTPA / ITO, which exhibits very low "on" and "off" voltages and excellent stability, making it a promising candidate for lightweight intelligent neuromorphic memory devices. Because this invention utilizes a pure polymer as the active layer, it can be fabricated into a nanoscale device using electron beam lithography and lift-off techniques. In contrast, products covalently grafted with two-dimensional materials, such as black phosphorus (BP) and graphene, may result in inhomogeneous lattice films when using the same techniques. The use of pure polymers effectively solves this problem. The PBDT-BDQTPA film of the device described in this invention exhibits uniform conductivity at the submicron scale, with a distance of approximately 40 nm between adjacent switching points. This indicates that the scaling limit of the polymer memristor of this invention can be extended to the 100 nm range, with a theoretical power consumption of approximately 10–20 J / bit. Such a small device is fabricated using electron beam lithography and lift-off methods in the form of an 8×8 cross-switch array, with word line and bit line widths of 100 nm and 200 nm, respectively, representing an extremely small nanoscale structure. This invention is the first in the world to fabricate an organic memristor device with a linewidth of 100 nanometers. It exhibits uniform memristor modulation in the scale range of hundreds of nanometers to hundreds of micrometers, with a device response time of less than 32 ns, power consumption of only 10 fJ / bit, cycle tolerance of more than 108 cycles, D2D performance parameter fluctuation between 3.12% and 8.45%, and a device yield of over 90%.

[0032] In summary, this invention holds promise for use in low-power nanoscale neuromorphic devices.

[0033] Beneficial technical effects of the present invention:

[0034] The present invention mentions a nanoscale neuromorphic memory with a novel DA-type two-dimensional conjugated symmetric polymer film as the active layer, which has the advantages of low power consumption and simple adjustability.

[0035] PBDT-BDQTPA and similar polymers, when used as active layers, exhibit good thermal stability and electrical properties.

[0036] This device is fabricated in the form of an 8×8 cross-switch array using electron beam lithography and a lift-off method. The word line and bit line widths are 100 nm and 200 nm, respectively, which are extremely small nanoscale structures. It has non-volatile memory rewriteability and a small threshold voltage, which has great advantages and wide applications in the field of next-generation low-power neuromorphic devices. Attached Figure Description

[0037] Figure 1 shows the Au / PBDT-BDQTPA / ITO device after 200 IV cycles.

[0038] Figure 2 shows the grazing incidence X-ray diffraction (GIXRD) pattern of the PBDT-BDQTPA thin film.

[0039] Figure 3 shows the effect of a 0.1V readout pulse (pulse width = 1μs; pulse period = 2μs) on the ON and OFF currents of the device under a constant voltage of 0.1V in both ON and OFF states over time.

[0040] Figure 4 shows the morphology test results of the Au / PBDT-BDQTPA / ITO device in the ON and OFF states using C-AFM.

[0041] Figure 5 shows the switching voltage and resistance distribution of the nanoscale PBDT-BDQTPA memristor device fabricated with an 8×8 cross-switch array.

[0042] Figure 6 is a schematic diagram of the structure of the polymer material PBDT-BDQTPA.

[0043] Figure 7 shows the structure of a nano-neuromorphic device with an organic two-dimensional conjugated symmetric polymer as the active layer.

[0044] Wherein: 1-SiO2 / Si substrate, 2-Ti / Au electrode, 3-active layer, 4-Ti / Au electrode.

[0045] Figure 8 shows the ON-state current mapping image of the nanoscale neuromorphic device fabricated based on PBDT-BDQTPA material.

[0046] Figure 9 is a schematic diagram of a neuromorphic device fabricated based on PBDT-BDQTPA material. Detailed Implementation

[0047] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the features and advantages of the present invention will become more apparent and understandable. Unless otherwise specified, all materials, reagents, etc., used in the following embodiments are commercially available.

[0048] Example 1: The synthesis of the polymer PBDT-BDQTPA in the active layer film of the present invention is illustrated by the following formula; the rest are similar methods: n ranges from ≥20.

[0049]

[0050] Specific synthesis steps:

[0051]

[0052] A solution of 2-alkylthiophene in tetrahydrofuran was added to a 100 mL reaction flask. Then, under argon protection, 18 mL of n-butyllithium (2.4 M) was added dropwise to the solution at low temperature; the mixture was then heated to 50 °C and stirred. Subsequently, 4,8-dehydrobenzo[1,2-b;4,5-b′]dithiophene-4,8-dione was added, and the mixture was reacted at 50-60 °C for another hour. After the reaction cooled to room temperature, SnCl₂·2H₂O dissolved in 32 mL of 10% HCl was added to the reaction, and the mixture was stirred for another 1-2 hours. After the reaction was complete, the solution was poured into ice water, yielding a pale yellow liquid. At 0 °C, the above compound was dissolved in THF and placed in a 150 mL flask. After bubbling with argon, 2.4 M n-butyllithium was added using a syringe. The reaction mixture was then stirred at ambient temperature. Subsequently, a hexane solution (1.0 M) of trimethyltinyl chloride was added, and the mixture was stirred at room temperature for another 1 hour to obtain a pale yellow solid.

[0053]

[0054] At 0 °C, 1,2-bis(4-(diphenylamino)phenyl)ethane-1,2-dione was dissolved in THF and placed in a 150 mL flask. After bubbling with argon, n-butyllithium (2.4 M) was added using a syringe. The reaction mixture was then stirred at ambient temperature. Subsequently, a hexane solution (1.0 M) of 3,6-bis(trimethyltinyl)phenyl-1,2-diamine was added, and the mixture was stirred at room temperature for another 1 hour to obtain a pale yellow solid.

[0055]

[0056] Equivalent amounts of the monomers and 10 mL of anhydrous toluene were added to a Schlenk flask. Argon gas was bubbled through the reaction mixture, followed by the addition of 20 mg of catalyst Pd(PPh3)4. The reaction mixture was vigorously stirred at high temperature under an inert atmosphere. After the reaction was complete, the reaction solution was poured into methanol, the precipitate was collected, and extracted with THF. The collected solid was then extracted with acetone using a Soxhlet extractor for 24 hours to remove oligomers and catalyst residues. Finally, the product was dried under vacuum overnight. The resulting two-dimensional conjugated polymer PBDT-BDQTPA was obtained.

[0057] Example 2: The method for preparing the organic nano-neuromyctic device with an organic two-dimensional conjugated symmetry polymer as the active layer according to the present invention includes the following steps:

[0058] 1) Form longitudinal and transverse electrode strips with a width of 100 nm and a spacing of 200 nm on a SiO2 / Si substrate.

[0059] 2) The bottom electrode strips were patterned using electron beam lithography with the Vistec EBPG-5200+ electron beam lithography system and electron beam evaporation of a 20nm Au layer on top of a 10nm Ti adhesion layer on a Denton electron beam evaporator.

[0060] 3) After lifting, spin-coat 50 μL of the toluene solution (5 mg / mL) of PBDT-BDQTPA prepared in Example 1 onto the Siwafer at 4000 rpm for 40 s, and then dry it thoroughly in a vacuum at 80 °C overnight.

[0061] 4) Finally, electron beam lithography, electron beam evaporation and lift-off are similarly used to pattern and deposit the top electrode consisting of 15 nm Ti and 45 nm Au, thereby completing the fabrication of the device and finally obtaining the device PBDT-BDQTPA.

[0062] Example 1

[0063] Figure 1 shows the current-voltage curves of the device fabricated above during 200 read-write-erase cycles. 200 consecutive current-voltage cycles were applied to the device, and it can be seen that the current-voltage curves exhibit great similarity during the 200-cycle "write-read-erase-read" process. The threshold voltages for both the ON and OFF states fluctuate within a very small range, while the resistance values ​​in the ON and OFF states also show a very stable state.

[0064] Example 2

[0065] Figure 2 shows the grazing incidence X-ray diffraction (GIXRD) pattern of the PBDT-BDQTPA thin film prepared above. The polymer film exhibits clear diffraction peaks, indicating that the polymer film has a highly ordered layered structure. Since the (010) diffraction peak is attributed to the π-π stacking of the polymer, this strong in-plane (010) diffraction peak indicates that the π-π stacking of the polymer is preferentially parallel to the substrate. Therefore, the GIXRD pattern of PBDT-BDQTPA shows that it has a highly ordered layered stacking with edge orientation. This molecular stacking at the edge can promote the transport of charge carriers, which is attributed to the fact that the π-π interchain stacking, intrachain conjugation, or a combination of both are parallel to the direction of the current. Therefore, this polymer has a small π-π stacking distance, which is beneficial to improving the intermolecular overlap integral and is expected to exhibit higher carrier mobility.

[0066] Example 3

[0067] As shown in Figure 3, the sensitivity of the fabricated device to switching on and off was tested by applying a pulsed voltage. The voltage pulse size was set to 0.1V, the duration to 1μs, and the pulse interval to 2μs. It can be seen that the current in the switching state of the device is within 10...8 The device was unaffected by the application of periodic pulse voltages, indicating that it is not sensitive to the read voltage.

[0068] Example 4

[0069] As shown in Figure 4, by integrating the sampled current along the scan length measured by C-AFM, a clear linear relationship between the current integral and the device size can be plotted, as shown in Figure 4. Extrapolation of the scale indicates that ultra-low operating current suitable for portable and low-power applications can be achieved in organic memristors below 10 nm.

[0070] Example 5

[0071] As shown in Figure 5, the open-circuit voltage and resistance distribution of the nanoscale PBDT-BDQTPA memristor device fabricated with an 8×8 cross-switch array are uniformly distributed and have the excellent characteristic of being rewritable multiple times.

[0072] Example 6

[0073] As shown in Figure 8, the fabrication method of the nanoscale PBDT-BDQTPA memristor device using an 8×8 cross-switch array includes the following steps:

[0074] 1) Form longitudinal and transverse electrode strips with a width of 100 nm and a spacing of 200 nm on a SiO2 / Si substrate.

[0075] 2) The bottom electrode strips were patterned using electron beam lithography with the Vistec EBPG-5200+ electron beam lithography system and electron beam evaporation of a 20nm Au layer on top of a 10nm Ti adhesion layer on a Denton electron beam evaporator.

[0076] 3) After lifting, spin-coat 50 μL of PBDT-BDQTPA in toluene (5 mg / mL) onto the Siwafer at 4000 rpm for 40 s, and then dry thoroughly in a vacuum at 80 °C overnight.

[0077] 4) Finally, electron beam lithography, electron beam evaporation and lift-off are similarly used to pattern and deposit the top electrode consisting of 15 nm Ti and 45 nm Au, thereby completing the fabrication of the device and finally obtaining the device PBDTR-DBQTPA.

[0078] Example 7

[0079] As shown in Figure 9, the conductivity of the PBDT-BDQTPA thin film of this device is uniform at the submicron scale, and the distance between adjacent switching points is approximately 40 nm. This indicates that the scaling limit of the polymer memristor of this invention can be extended to the 100 nm range, with a theoretical power consumption of approximately 10–20 J / bit. Such a small device is fabricated in the form of an 8×8 cross-switch array using electron beam lithography and a lift-off method, with word line and bit line widths of 100 nm and 200 nm, respectively, representing an extremely small nanoscale structure.

[0080] This invention provides a nano-neuromorphic device with an organic two-dimensional conjugated symmetric polymer as the active layer. The specific preparation method of different alkyl R-group derivatives of the polymer PBDT-BDQTPA is shown in Example 1. Correspondingly, the specific preparation method of the nano-neuromorphic device with an organic two-dimensional conjugated symmetric polymer as the active layer is shown in Example 2. Furthermore, the corresponding experimental data and effect data of Examples 1-7 are almost the same, and will not be repeated here.

[0081] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

[0082] The preparation steps, effect examples, and accompanying data described above are preferred embodiments of the present invention. Other embodiments within the scope of protection can also achieve the above-mentioned beneficial effects, and will not be repeated here. It should be noted that those skilled in the art can make several improvements and modifications without departing from the concept of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A nano-neuromyctic device using an organic two-dimensional conjugated symmetry polymer as the active layer, characterized in that, It has a sandwich structure, with a horizontal electrode in the first layer, a polymer PBDT-BDQTPA thin film in the middle, and a vertical electrode in the third layer; the structure of the polymer PBDT-BDQTPA thin film is shown in the following formula: 。 2. The nano-neuromyctic device with an organic two-dimensional conjugated symmetry polymer as the active layer according to claim 1, characterized in that, The conductivity of the PBDT-BDQTPA thin film of the nano-neuromorphic device is uniform at the submicron scale, the distance between adjacent switching points is 40 nm, and the scaling limit of the nano-neuromorphic device is 100 nm.

3. The nano-neuromyctic device with an organic two-dimensional conjugated symmetry polymer as the active layer according to claim 1, characterized in that, The nano-neuromorphic device is fabricated in the form of an 8×8 cross-switch array using electron beam lithography and a lift-off method, with word line and bit line widths of 100 nm and 200 nm, respectively.

4. The nano-neuromyctic device with an organic two-dimensional conjugated symmetry polymer as the active layer according to claim 1, characterized in that, The nano-neuromorphic device has a non-volatile rewritable storage function: the device exhibits different resistance states under different voltages, which are defined as "0" and "1" in binary to store data, and the data can still be saved after power failure.

5. A method for fabricating a nano-neuromorphic device with an organic two-dimensional conjugated symmetry polymer as the active layer according to any one of claims 1-4, comprising the following steps: (1) forming longitudinal and transverse electrode strips with a width of 50-100 nm and a spacing of 150-200 nm on a SiO2 / Si substrate; (2) performing electron beam lithography using an electron beam lithography system and depositing a 15-20 nm Au layer on a 5-10 nm Ti adhesion layer using an electron beam evaporator to pattern the bottom electrode strips; (3) after lifting, spin-coating a 50-80 µL toluene solution (5 mg / mL) of PBDT-BDQTPA onto the bottom electrode strips at a speed of 1000-3000 rpm for a spin-coating time of 50-100 rpm. s, and then thoroughly dry overnight in a vacuum at 50-100°C; (4) Finally, similarly use electron beam lithography, electron beam evaporation and stripping to pattern and deposit a top electrode consisting of 10-15nm Ti and 40-50nm Au, thereby completing the fabrication of the device and finally obtaining the device PBDT-BDQTPA.

6. A testing method for a nano-neuromorphic device using an organic two-dimensional conjugated symmetric polymer as the active layer according to claim 1, comprising the following steps: 1) all electrical measurements used to fabricate the device are performed on a Keithley 4200 semiconductor parameter analyzer equipped with a pulse measurement unit, thereby further protecting the device under these environmental conditions; 2) in C-AFM measurement, a PBDT-BDQTPA film is spin-coated onto a glass substrate coated with ITO; 3) finally, a bias voltage is directly applied to the polymer film using a Pt-coated C-AFM tip as a movable top electrode to complete the morphology test of the device.

7. The application of the nano-neuromorphic device with an organic two-dimensional conjugated symmetry polymer as the active layer as described in any one of claims 1-4 in the field of low-power information storage.

8. The application of the nano-neuromorphic device with an organic two-dimensional conjugated symmetry polymer as the active layer as described in claim 7 in the field of low-power information storage, characterized in that, The device exhibits different resistance states under different voltages. These states are defined as "0" and "1" in binary to store data. The data can still be preserved after power is turned off, thus exhibiting uniform resistance switching characteristics and possessing excellent characteristics of ultra-miniaturization and low power consumption.

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