Micro-electro-mechanical system based impact printing nanoliter droplet generation method

Abstract

This invention discloses a method for generating nanoscale droplets through impact printing based on microelectromechanical systems (MEMS), belonging to the field of MEMS technology. The method includes: constructing an actuator with a flexible membrane containing reinforcing ribs; applying a controlled voltage ramp to allow the membrane to slowly store energy and lock the pre-deformation displacement based on real-time capacitance values; rapidly cutting off the voltage to cause the membrane to rebound towards a microfluidic cavity with high acceleration under elastic restoring force, generating a high-energy shock wave; driving the fluid to overcome viscous resistance and eject to form droplets; and capturing residual vibration data to dynamically adjust the voltage to achieve closed-loop feedback. This method can generate a steep pressure wave front, effectively shearing high-viscosity fluid bridges and eliminating satellite droplets, ensuring long-term consistency and precise resolution of droplet volume; and solving the problems of insufficient kinetic energy and poor consistency in the distribution of high-viscosity fluids.

Description

Technical Field

[0001] This invention relates to the field of microelectromechanical systems (MEMS) technology, specifically a method for generating nanoscale droplets by impact printing based on MEMS. Background Technology

[0002] With the rapid development of microelectromechanical systems (MEMS) technology, high-precision fluid distribution technology has been widely applied in fields such as precision electronics manufacturing, biomedical printing, and additive manufacturing. Microdroplet jetting technology, by precisely controlling the jetting volume and frequency of fluid, can achieve quantitative deposition of nano- and even pico-level droplets, becoming a core means to improve the precision of industrial manufacturing and the molding quality of bioactive materials. In these application scenarios, achieving compatibility with various complex materials and ensuring a high degree of consistency in the jetting process are key dimensions for evaluating the performance of current microfluidic driven systems.

[0003] Among these, pulse-driven jetting technology based on flexible diaphragm deformation is a common approach for generating nano-scale droplets. This technology uses an actuator to mechanically deform the diaphragm above the microfluidic cavity, utilizing the instantaneously generated pressure wave within the cavity to overcome the surface tension of the fluid, causing the fluid to be ejected at high speed through the nozzle to form independent droplets. For the printing requirements of high-viscosity bio-inks or functional pastes, the system typically needs to possess extremely high instantaneous acceleration and kinetic energy transfer efficiency to ensure that fluid bridges can rapidly break and maintain morphological stability under strong viscosity resistance environments.

[0004] However, existing driving schemes are limited by the actuator's response frequency and deformation rate, resulting in insufficiently steep pressure wave rise edges when handling high-viscosity fluids. This leads to insufficient jet kinetic energy to overcome the fluid's internal viscous forces, easily generating long filamentous tails or numerous parasitic satellite droplets. Furthermore, traditional open-loop drive modes cannot sense the actual displacement state of the diaphragm, and are susceptible to mechanical fatigue and environmental temperature fluctuations, resulting in poor droplet volume accuracy and jet consistency over long-term operation. In addition, the lack of an effective feedback adjustment mechanism makes it difficult for the system to compensate for nonlinear changes in fluid characteristics in real time, leading to inaccurate matching between the jet pulse and the fluid supply state, severely impacting the reliability and resolution of the micro-jet system. Summary of the Invention

[0005] The purpose of this invention is to provide a method for generating droplets in impact printing based on microelectromechanical systems, which can effectively solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for generating droplets in impact printing based on microelectromechanical systems (MEMS) includes the following specific steps: Step 1: Constructing an actuator: An actuator structure comprising a microfluidic cavity, a nozzle, and a flexible vibrating membrane covering the microfluidic cavity is constructed using micromachining technology. The surface of the flexible vibrating membrane is distributed with reinforcing ribs to enhance structural rigidity. The flexible vibrating membrane is arranged parallel to a fixed electrostatic driving electrode as a movable electrode, forming a capacitive driving unit with an initial gap. Step 2: Controlled energy storage: An initial bias voltage with a controlled ramp rate is applied to the electrostatic driving electrode. The flexible vibrating membrane is driven by electrostatic attraction to undergo slow elastic deformation away from the bottom of the microfluidic cavity. The real-time capacitance value between the flexible vibrating membrane and the electrostatic driving electrode is monitored in real time, and the flexible vibrating membrane is locked based on the real-time capacitance value. Step 3: Ultrafast Triggering: At a preset injection triggering moment, the initial bias voltage is turned off within a preset time constant, causing the flexible vibrating membrane to rebound towards the microfluidic cavity with an instantaneous acceleration not less than a preset acceleration threshold under the drive of its stored elastic restoring force, thereby generating a high-energy shock wave on the fluid in the microfluidic cavity with a viscosity greater than a preset viscosity threshold; Step 4: Droplet Generation: The high-energy shock wave drives the fluid to overcome surface tension and viscous resistance, ejecting it from the nozzle and forming droplets of a predetermined volume level without satellite droplets; Step 5: Closed-Loop Feedback Adjustment: The residual vibration data of the flexible vibrating membrane after rebound is captured using the real-time capacitance value, and the fluid state changes in the microfluidic cavity are analyzed based on the residual vibration data to dynamically adjust the ramp rate or voltage amplitude of the initial bias voltage in the next injection cycle.

[0008] Preferably, in step 1, the microfluidic cavity of the actuator is formed on a single-crystal silicon substrate using deep reactive ion etching (DRIE), and its inner wall has a geometric structure within a preset error range. The flexible vibrating diaphragm is made of low-stress silicon nitride material and is prepared by plasma-enhanced chemical vapor deposition (PECVD). The film thickness is controlled within a preset thickness range to ensure sufficient mechanical strength and excellent elastic recovery characteristics. The reinforcing ribs are radially and uniformly distributed on the surface of the flexible vibrating diaphragm and are integrally formed with the flexible vibrating diaphragm body through a stepwise PECVD process. These radial reinforcing ribs can effectively suppress the higher-order vibration modes of the flexible vibrating diaphragm during high-speed rebound, ensuring that energy is concentrated in the main vibration direction of the piston, thereby improving the transmission efficiency of pressure waves.

[0009] Preferably, in step 2, the controlled pressure ramp rate is set such that the rising speed of the flexible vibrating diaphragm is always lower than the critical value of the fluid replenishment speed within the microfluidic cavity. Because high-viscosity fluids experience significant flow resistance within microchannels, excessively rapid lifting of the flexible vibrating diaphragm can cause a sudden drop in pressure within the microfluidic cavity, leading to the generation of cavitation bubbles and severely interfering with the consistency of the jetting. This solution controls the pressure ramp rate within a preset rate of change threshold, providing sufficient replenishment time for the fluid and ensuring that the microfluidic cavity remains fully filled during the energy storage phase. Real-time capacitance monitoring is achieved through a high-precision capacitance detection chip integrated into the drive circuit. Its sampling frequency reaches a preset sampling frequency, and its displacement measurement resolution is better than a preset resolution threshold, ensuring precise control of the spatial position of the flexible vibrating diaphragm.

[0010] Preferably, in step 3, the initial bias voltage is turned off through a fast discharge circuit connected in parallel across the electrostatic drive electrode. This circuit has extremely low equivalent series resistance and parasitic inductance, and can release the charge accumulated on the electrode surface within a preset time threshold. Due to the extremely short turn-off time, the flexible vibrating diaphragm releases its stored elastic potential energy the instantaneously after being released from electrostatic constraints, generating an instantaneous acceleration that reaches the target peak value. The steep pressure wave front formed by this high acceleration is key to shearing the high-viscosity fluid bridge, effectively counteracting the intermolecular viscous forces within the fluid, and enabling the droplet to break instantaneously at the nozzle outlet.

[0011] Preferably, in step 4, for bio-inks or conductive pastes within a preset viscosity range, the inner diameter of the nozzle is set within a preset orifice diameter range. The inner wall and outlet end face of the nozzle are coated with an anti-slip coating of a preset thickness range, which works synergistically with the high-acceleration rebound of the flexible vibrating membrane. When the shock wave reaches the nozzle, the fluid not only gains outward momentum, but also exhibits significant shear thinning characteristics due to the extremely high strain rate, greatly reducing jet resistance. By adjusting the off-phase of the initial bias voltage, the volume of a single droplet can be precisely controlled within the target volume range.

[0012] Preferably, in step 5, the residual vibration data includes the oscillation frequency, damping ratio, and equilibrium position offset of the flexible vibrating diaphragm after spraying. When changes in ambient temperature cause fluctuations in fluid viscosity, the damping of the flexible vibrating diaphragm in the fluid changes accordingly, resulting in a shift in the residual vibration decay time and oscillation frequency. The digital signal processing unit inside the control system processes the acquired capacitance signal and extracts the characteristic frequency. If the amplitude of the rebound residual vibration is detected to exceed a preset threshold, the system will apply a reverse pulse voltage with opposite phase during the first oscillation cycle after the voltage is turned off, utilizing reverse electrostatic attraction to achieve active vibration damping, thereby shortening the system preparation time and increasing the maximum spraying frequency to the target frequency.

[0013] Preferably, the real-time capacitance value locking mechanism continuously compares the current capacitance value with a set target value through a comparator circuit. When the flexible diaphragm is stretched upward to a preset position corresponding to the target capacitance value, the drive circuit automatically enters a voltage holding mode. This pre-deformation control method based on capacitance feedback can eliminate the mechanical fatigue effect caused by the increase of the driver material over time. Even after a predetermined number of spray cycles, the displacement accuracy deviation of the flexible diaphragm remains within the preset allowable deviation range, ensuring the stability of long-term industrial production.

[0014] Preferably, the method achieves large-scale integrated printing through a multi-channel parallel control architecture. Each jetting unit has an independent capacitance monitoring link, enabling individualized compensation for fluid resistance differences at different physical locations. When processing bio-ink containing living cells, the duration of the high-energy shock wave is controlled within a preset duration threshold to ensure that the shear force acting on the cell membrane is far below the damage threshold, thereby maintaining the predetermined cell viability.

[0015] Preferably, the sidewall of the microfluidic cavity is provided with a functional layer with gradient wettability. The end of the functional layer near the flexible vibrating membrane is oleophilic, and the end near the nozzle is oleophobic. This structural design, combined with the directional shock wave generated by the flexible vibrating membrane, can further induce the fluid to converge towards the central axis of the nozzle, reducing energy dissipation on the sidewall, and enabling the smooth ejection of ultra-high viscosity fluids under a relatively low driving voltage.

[0016] Preferably, the amplitude of the initial bias voltage is adjusted nonlinearly based on the real-time viscosity of the fluid to be printed. For a fluid with a first preset viscosity, the initial bias voltage is set to the first preset voltage; when the viscosity increases to a second preset viscosity, the control system automatically increases the voltage to the second preset voltage based on empirical curves in the historical database to increase the elastic prestress. This adaptive adjustment mechanism enables the method to be compatible with a very wide range of materials, from water-based solvents to high-fill-rate metal pastes.

[0017] Preferably, the displacement sensor of the flexible vibrating diaphragm is not limited to capacitance detection. A piezoresistive strain gauge sensor is also integrated into the edge region of the flexible vibrating diaphragm, and the piezoresistive strain gauge sensor and the capacitance sensor constitute a dual-modal sensing system. When the capacitance signal is disturbed by environmental fluctuations, the system automatically switches to the piezoresistive signal for calibration, ensuring robustness of detection in complex production environments.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] Breakthrough fluid viscosity compatibility: This invention combines a high-rigidity diaphragm with an ultrafast discharge circuit to generate extremely high instantaneous acceleration, resulting in a pressure wave with an exceptionally steep rise edge. This energy release method generates mechanical impacts sufficient to overcome strong intermolecular forces, successfully achieving precise micro-dispensing of fluids in the high viscosity range. In contrast, traditional piezoelectric or thermal bubble-driven technologies often suffer from clogging due to insufficient kinetic energy when handling such materials. This invention significantly broadens the range of materials applicable to the micro / nano manufacturing field.

[0020] The extremely high droplet morphology control quality is achieved due to the concentrated energy release within a very short time, resulting in a highly concentrated momentum distribution at the nozzle and a large waveform slope during droplet formation, which can rapidly cut off liquid bridges. The generated droplets exhibit excellent spherical geometry and effectively eliminate satellite droplet phenomena. This high-quality droplet formation characteristic is of great significance for the precision wiring of flexible electronic circuits and the fine stacking of biological tissues, avoiding short circuits or structural contamination caused by parasitic droplets.

[0021] Long-term printing consistency and stability are ensured by introducing a high-frequency capacitive closed-loop feedback mechanism that can sense the real displacement of the flexible vibrating diaphragm in real time, automatically compensating for fluid viscosity changes caused by environmental fluctuations and mechanical fatigue wear of the flexible diaphragm. By locking the pre-deformation displacement in real time, the consistency error of droplet volume is controlled within a preset deviation range, ensuring that printing accuracy does not drift during long-term jetting cycles.

[0022] With precise volumetric resolution, this invention utilizes capacitive monitoring technology to achieve extremely high displacement locking accuracy. By adjusting the initial deformation of the diaphragm, it achieves digital control of the droplet volume, with volumetric resolution reaching the predetermined micro-level. Combined with an anti-drip coating at the nozzle, the drip-breaking effect is further improved, increasing production efficiency while maintaining accuracy. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall technical solution architecture of the impact printing nano-scale droplet generation method based on microelectromechanical systems proposed in this invention;

[0024] Figure 2 This is a schematic diagram of the core principle framework of the present invention based on electrostatic pre-deformation energy storage and ultrafast release to generate shock waves;

[0025] Figure 3 This is a flowchart outlining the main stages of this invention, from actuator construction and controlled energy storage to closed-loop feedback regulation.

[0026] Figure 4 This is a schematic diagram of the multi-level interaction relationship and data flow between real-time capacitor monitoring feedback and dynamic compensation of drive control parameters in this invention;

[0027] Figure 5 This is a schematic diagram comparing the core principle of this invention with existing technologies in terms of the steepness of the pressure wave front and the drip-breaking effect of high-viscosity fluids. Detailed Implementation

[0028] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0029] Example 1

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0031] See Figures 1-5 In the aforementioned microelectromechanical system (MEMS)-based impact printing method for generating nano-scale droplets, step 1, the process of constructing the actuator, involves high-precision micro-nano fabrication techniques. The microfluidic cavity of the actuator is formed on a single-crystal silicon substrate using deep reactive ion etching (DRIE). In this process, the geometric contour of the microfluidic cavity is first defined on the surface of the single-crystal silicon wafer using photolithography, and then extended downwards using high-selectivity plasma dry etching technology to form a cavity structure with vertical sidewalls. The depth of the microfluidic cavity is controlled between 50 micrometers and 200 micrometers, and its bottom geometry is optimized to reduce dead zones for fluid flow. At the center of the bottom of the microfluidic cavity, a nozzle is formed by laser drilling or reactive ion etching, and the inner diameter of the nozzle is set within the range of 5 micrometers to 30 micrometers according to the target droplet volume.

[0032] The flexible vibrating membrane covers the microfluidic cavity, serving both sealing and kinetic energy transfer functions. The flexible vibrating membrane is made of low-stress silicon nitride and fabricated using plasma-enhanced chemical vapor deposition (PECVD). In this process, the residual stress of the film is controlled to a tensile stress state below 50 MPa by precisely adjusting the flow ratio of ammonia to silane and the radio frequency power, ensuring that the membrane maintains good flatness even after repeated reciprocating motions. The thickness of the flexible vibrating membrane is set between 0.5 micrometers and 2 micrometers, and its mechanical strength is enhanced by a surface-distributed reinforcing rib structure.

[0033] The reinforcing ribs are radially and uniformly distributed on the surface of the flexible vibrating diaphragm, and are integrally formed with the flexible vibrating diaphragm body through a stepwise chemical vapor deposition process. Specifically, after depositing a silicon nitride film of basic thickness, the radial rib regions are defined by secondary photolithography, and a second silicon nitride layer with a thickness of 0.5 micrometers to 1 micrometer is deposited. This radial reinforcing rib effectively suppresses the higher-order vibration modes of the flexible vibrating diaphragm during high-speed rebound, ensuring that energy is concentrated in the main vibration direction of the piston, thereby improving the transmission efficiency of pressure waves. The flexible vibrating diaphragm serves as a movable electrode, and its surface is covered with a 100-nanometer-thick aluminum or gold conductive layer through a sputtering process.

[0034] The fixed electrostatic driving electrode is disposed above the flexible vibrating diaphragm, and a predetermined initial gap is maintained between them by a silicon dioxide sacrificial layer or micro-machined pillars. This gap is typically between 2 and 10 micrometers. The electrostatic driving electrode and the flexible vibrating diaphragm together constitute a capacitive driving unit.

[0035] In step 2, controlled energy storage, an initial bias voltage with a controlled ramp rate is applied to the electrostatic drive electrode. The ramp rate of the initial bias voltage is set to 5V / μs, a value optimized through dynamic simulation to ensure that the rising speed of the flexible vibrating membrane is always lower than the critical value of the fluid replenishment rate within the microfluidic cavity. Because high-viscosity fluids (such as 150cP conductive silver paste) have significant flow resistance within the microchannel, if the flexible vibrating membrane rises too quickly, it will cause a sudden drop in pressure inside the microfluidic cavity, leading to the generation of cavitation bubbles. By controlling the ramp rate within a preset rate-of-change threshold, sufficient fluid replenishment time is provided, ensuring that the microfluidic cavity remains fully filled throughout the energy storage phase.

[0036] During the voltage boosting process, the system uses a high-precision capacitance detection chip integrated in the drive circuit to monitor the real-time capacitance value between the flexible diaphragm and the electrostatic drive electrode at a sampling rate of 20MHz. The real-time capacitance value... With the pre-deformation position of the flexible vibrating diaphragm Satisfy the following mathematical relationship:

[0037]

[0038] in, The dielectric constant of the medium between the electrodes. For the effective overlapping area, This is the initial gap. The control system accurately determines the diaphragm position by monitoring changes in capacitance. The diaphragm is positioned when the capacitance reaches the target capacitance value corresponding to a target displacement of 2.2 micrometers. At this time, the drive circuit automatically enters the voltage holding mode to lock the pre-deformation displacement of the flexible diaphragm.

[0039] In step 3, the ultrafast triggering, at a preset injection triggering moment, the control circuit, through a fast-discharge MOS transistor circuit connected in parallel across the electrostatic drive electrode, turns off the initial bias voltage within a time constant of less than 10 microseconds (4.5 microseconds in this embodiment), i.e., the voltage rapidly drops to 0V. This fast-discharge circuit has extremely low equivalent series resistance and parasitic inductance, enabling it to release the charge accumulated on the electrode surface in a very short time. Due to the extremely short turn-off time, the flexible vibrating diaphragm releases its stored elastic potential energy the instant it is released from electrostatic constraints, generating an instantaneous acceleration of approximately 1.2 × 10^5 m / s² as it rebounds towards the microfluidic cavity.

[0040] The steep pressure wave front generated by this high acceleration can produce instantaneous pressures on the order of megapascals. According to Newton's second law, the impact force exerted on the fluid by the flexible diaphragm upon its rebound is... satisfy:

[0041]

[0042] in, For the effective quality of the diaphragm, For instantaneous acceleration, Let be the equivalent stiffness coefficient of the diaphragm. This is a pre-deformation displacement. The resulting shock wave is sufficient to shear bridges in silver paste with a viscosity as high as 150 cP, effectively counteracting the strong intermolecular viscous forces within the fluid.

[0043] In step 4, droplet generation, the high-energy shock wave is transmitted to the nozzle via fluid. For high-viscosity conductive silver paste, the inner wall and outlet face of the nozzle are coated with a polytetrafluoroethylene (PTFE) anti-fouling coating with a nanometer-thickness. When the shock wave reaches the nozzle, the fluid not only gains outward momentum, but also exhibits significant shear-thinning characteristics due to the extremely high strain rate, greatly reducing jet resistance. The droplet volume can be fine-tuned by adjusting the phase of the initial bias voltage's turn-off time relative to the capacitance peak. In this embodiment, by controlling the pre-deformation displacement at 2.2 micrometers, nano-liter droplets with a volume accuracy better than 5 pL were successfully generated, ranging in volume from 5 pL to 20 pL, with no parasitic satellite droplets behind the main droplet.

[0044] In step 5, closed-loop feedback adjustment, the residual vibration data of the flexible diaphragm after rebound is captured using the real-time capacitance value. This residual vibration data includes the oscillation frequency, damping ratio, and equilibrium position offset. The digital signal processing unit (DSP) inside the control system performs a Fast Fourier Transform (FFT) on the capacitance signal at a 20MHz sampling rate, extracts the characteristic frequencies, and analyzes the change in the damping ratio ζ in the residual vibration data. Subsequently, the system uses the formula Calculate the required voltage compensation amount ,in The system uses a preset compensation coefficient and verifies and fine-tunes the compensation amount based on a pre-stored three-dimensional compensation lookup table of "residual vibration frequency-viscosity-bias voltage". When the ambient temperature increases, causing the silver paste viscosity to decrease, the fluid's damping on the diaphragm decreases, resulting in a longer decay time for residual vibration and a shift in the oscillation frequency. Based on the feedback, the system automatically reduces the initial bias voltage amplitude of the next injection cycle by 3% to offset the energy excess caused by the decrease in viscosity and maintain the consistency of droplet volume.

[0045] Example 2

[0046] See Figures 1-5 This embodiment focuses on describing the application details of this method in the precision printing scenario of bio-ink. In step 1, during the actuator construction stage, the sidewall of the microfluidic cavity is provided with a functional layer with gradient wettability. The functional layer is prepared by a self-assembled monolayer (SAMs) process, with the end near the flexible vibrating membrane being oleophilic (contact angle less than 30 degrees) and the end near the nozzle being oleophobic (contact angle greater than 110 degrees). This structural design, combined with the directional shock wave generated by the flexible vibrating membrane, can further induce the bio-ink to converge towards the central axis of the nozzle, reducing energy dissipation on the sidewall, thus enabling the smooth ejection of ultra-high viscosity fluid under a relatively low driving voltage.

[0047] In the controlled energy storage step 2, for the bio-ink containing live cells with a viscosity of 300 cP, the initial bias voltage ramp rate is further slowed to 2 V / μs. At this point, the control system locks the pre-deformation displacement of the membrane at 3.5 micrometers using capacitance monitoring technology. Since bio-ink is highly sensitive to shear forces, the smoothness of the energy storage process is crucial for maintaining cell viability. The real-time capacitance value monitoring sampling frequency is maintained at 20 MHz to ensure that the driving voltage smoothly enters the holding phase when the displacement approaches the locked target value, avoiding membrane oscillations caused by overshoot.

[0048] In step 3, the ultrafast triggering, the on-resistance of the fast discharge circuit is precisely controlled to within 0.5 ohms to ensure that the charge is released within 3 microseconds. The duration of the pressure wave generated by the flexible vibrating membrane at the moment of rebound is strictly controlled to within 15 microseconds. This duration threshold ensures that the instantaneous shear force acting on the cell membrane in the bio-ink is far below the threshold that would cause cell damage, thereby maintaining the predetermined cell viability (tested to be greater than 95%).

[0049] In step 4, droplet generation, the high-energy shock wave drives 300 cP of bio-ink to be ejected from a nozzle with a diameter of 25 micrometers. Due to the complex polymer components in the bio-ink, it exhibits significant elastic recovery characteristics during ejection. In this embodiment, by applying a nanoscale hydrophobic coating at the nozzle exit and combining it with the high-acceleration rebound generated by the membrane, the instantaneous breakage of the liquid bridge at the nozzle is achieved. By adjusting the turn-off phase of the initial bias voltage, the volume of a single droplet is controlled between 10 pL and 20 pL.

[0050] In step 5, closed-loop feedback regulation, a nonlinear mapping adjustment algorithm is introduced to address the characteristics of bio-inks, such as sedimentation or slight viscosity fluctuations over time. The system retrieves the corresponding viscosity compensation curve from the controller's historical database based on the captured changes in the residual vibration damping ratio. When a decrease in residual vibration frequency is detected (indicating an increase in effective fluid mass or viscosity), the control system automatically increases the initial bias voltage amplitude for the next cycle by 5% to increase the elastic prestress of the diaphragm, compensate for energy loss caused by fluid damping, and ensure that the droplet volume deviation remains within ±1.5% during several hours of continuous printing.

[0051] Example 3

[0052] See Figures 1-5This embodiment details a large-scale integrated printing implementation scheme achieved through a multi-channel parallel control architecture. In step 1, the actuator structure is designed as a linear array with 1024 independent jetting units. Each jetting unit has an independent flexible vibrating diaphragm, an electrostatic drive electrode, and a microfluidic cavity. To ensure consistency between channels, the flexible vibrating diaphragm is fabricated using a uniform chemical vapor deposition process, but a piezoresistive strain gauge sensor is additionally integrated into the edge region of each diaphragm. The piezoresistive strain gauge sensor and the capacitive sensor constitute a dual-modal sensing system.

[0053] In the controlled energy storage stage of step 2, the initial bias voltages of the 1024 channels are supplied in parallel by a high-performance multi-channel digital-to-analog converter (DAC). Due to the different physical locations of each channel (such as the pressure difference between the end and near ends of the flow channel), there are slight differences in the fluid supply rate. The system uses real-time capacitance value feedback to independently set the boost slope for each channel. For units at the end of the flow channel, the boost slope is appropriately reduced to prevent cavitation. The locking mechanism continuously compares the current capacitance value of each channel with the independent target value set for that channel through a comparator circuit. When the diaphragm of a certain channel reaches a predetermined position, the corresponding channel drive switch automatically switches to the voltage holding branch.

[0054] In the ultrafast triggering stage of step 3, each channel is equipped with an independent fast-discharge MOSFET. After receiving the global trigger signal, each channel fine-tunes the discharge delay based on the capacitance feedback value at that moment. If the capacitance value of a certain channel deviates from the target value due to environmental interference, the system will perform phase compensation on the discharge moment within a sub-microsecond timescale to ensure that the leading edge of the pressure wave generated by all channels is synchronized.

[0055] In step 4, droplet generation, to address the issue of decreased fluid viscosity due to heat accumulation caused by large-scale integration, the fluid state is monitored in real time at the nozzles of each unit. Thanks to the use of an anti-leaking nano-coating and a high-acceleration rebound mechanism, droplet formation consistency across channels under the same driving parameters is ensured.

[0056] In step 5, closed-loop feedback adjustment, the digital signal processing unit in the multi-channel parallel control architecture performs time-division multiplexing processing on the 1024 capacitor signals. The system analyzes the residual vibration data of each channel in real time to establish a "viscosity distribution heatmap" for the entire array. If a temperature increase in the central region of the array is detected, leading to a local decrease in viscosity, the system automatically lowers the initial bias voltage amplitude of each injection unit in that region. This individualized compensation mechanism ensures that even in complex production environments, the droplet volume uniformity of the entire array remains better than 2%. When the capacitor signal fluctuates significantly due to external electromagnetic interference, the system automatically switches to the piezoresistive strain signal for displacement calibration and adjustment, ensuring that the detection system has extremely high robustness.

[0057] Example 4

[0058] See Figures 1-5 This embodiment describes a printing implementation for extremely high-viscosity materials (such as 500 cP metal paste). In step 1, when constructing the actuator, the reinforcing ribs of the flexible vibrating diaphragm are designed with a high-density mesh distribution, made of high-modulus silicon carbide, and integrally formed via low-pressure chemical vapor deposition (LPCVD). This structure significantly improves the diaphragm's equivalent stiffness coefficient, enabling it to withstand higher electrostatic attraction without plastic deformation.

[0059] In the controlled energy storage step 2, the initial bias voltage is boosted to a high voltage state exceeding 200V. To prevent air breakdown, the drive unit is sealed in an environment filled with a high-insulation-strength gas (such as sulfur hexafluoride). Due to the extremely slow 500cP slurry replenishment, the voltage ramp rate is strictly controlled at 1V / μs, and the pre-deformation displacement of the diaphragm is locked at a critical position of 5 micrometers to accumulate sufficient elastic potential energy. The displacement measurement resolution of the real-time capacitance monitoring system is optimized to the 5-nanometer level.

[0060] In step 3, ultrafast triggering, a silicon carbide power device is used to construct the discharge path, reducing the turn-off time to less than 2 microseconds. The instantaneous acceleration generated by the diaphragm at the moment of release reaches 2.5 × 10^5 m / s². According to the principles of wave dynamics, the shock wave formed by this ultra-high acceleration propagates in the slurry and can instantly break through the network resistance between high-concentration metal particles.

[0061] In step 4, droplet generation, a functional layer with an oleophilic / oleophobic gradient is introduced into the nozzle sidewall to induce the high-viscosity slurry to converge toward the nozzle axis. Under the action of the shock wave, the slurry undergoes extreme shear thinning behavior at the nozzle orifice, and the instantaneous apparent viscosity is reduced to less than 10% of its original value, thereby achieving stable nano-level spraying of 500 cP slurry.

[0062] In step 5, the closed-loop feedback adjustment, due to the extremely high damping of the high-viscosity slurry, the residual vibration disappears rapidly. The system employs highly sensitive capacitance change rate monitoring technology (dC / dt) to capture the minute overshoot signal after the diaphragm rebounds. Based on this signal, the control system dynamically adjusts the boost parameters for the next pulse in real time. If the slurry viscosity further increases due to solvent evaporation, the system automatically triggers a voltage compensation mechanism, linearly increasing the initial bias voltage from 200V to 220V to ensure that printing accuracy remains constant during long-term operation. This adaptive adjustment mechanism enables this method to be compatible with a very wide range of materials, from low-viscosity aqueous solvents to extremely high-fill-rate metal slurries.

[0063] Example 5

[0064] See Figures 1-5This embodiment details an implementation scheme for dispensing adhesive onto precision optical lenses. In step 1, the microfluidic cavity volume of the actuator is miniaturized to reduce the influence of fluid inertia on the frequency response. The nozzle inner diameter is set to 10 micrometers, and the nozzle outlet has a rounded transition structure to optimize the flow field distribution.

[0065] In the controlled energy storage step 2, to achieve precise control of the lens curvature, a single injection of an extremely small volume of liquid droplet is required. The system precisely locks the pre-deformation displacement of the flexible vibrating diaphragm at 0.8 micrometers. At this point, the capacitance detection chip suppresses common-mode noise through a differential detection circuit, ensuring sensing accuracy at sub-micrometer displacements. The boost slope is set to 3V / μs based on the rheological properties of the lens adhesive to ensure no microbubbles are generated within the cavity.

[0066] In step 3, the ultrafast triggering, the discharge circuit returns the voltage to zero within 5 microseconds. The 1.0 × 10⁵ m / s² acceleration generated by the diaphragm acts on the optical adhesive, producing a high-frequency pressure pulse. In step 4, the droplet detaches from the nozzle with extremely high kinetic energy, overcoming the high surface tension of the adhesive. By controlling the phase relationship between the turn-off time and the capacitor sampling clock, the droplet volume stepping accuracy is controlled within 0.2 pL.

[0067] In step 5, the closed-loop feedback adjustment, the digital signal processing unit monitors the zero-point offset of the diaphragm in real time after rebound. If the diaphragm fails to return to its initial equilibrium position, it indicates that there is residual liquid at the nozzle. The system immediately applies a high-frequency micro-amplitude oscillation voltage in the next non-jet cycle to remove the residual liquid through micro-mechanical vibration, ensuring the long-term self-cleaning capability of the printhead and the consistency of jetting accuracy.

[0068] Example 6

[0069] See Figures 1-5 This embodiment describes a printing stability control scheme for scenarios with drastic fluctuations in ambient temperature. During the actuator construction in step 1, thin-film thermistors are integrated around the flexible vibrating diaphragm to sense the local fluid temperature in real time.

[0070] In the controlled energy storage step 2, the control system not only locks the diaphragm displacement based on capacitor feedback, but also queries the pre-stored three-dimensional compensation table of "temperature-viscosity-driving voltage" in real time, based on the temperature data from the thermistor feedback. When the ambient temperature rises from 25 degrees Celsius to 40 degrees Celsius, since the fluid viscosity typically decreases exponentially, the system automatically calculates the lower elastic potential energy required at this time.

[0071] In step 3, the ultrafast triggering process, the system adjusts the gate drive current of the MOSFET based on real-time capacitor feedback to fine-tune the damping characteristics of the discharge circuit. This ensures that the time constant of charge release remains at the ideal value of 4.5 microseconds at different temperatures, avoiding acceleration fluctuations caused by temperature drift of circuit parameters.

[0072] In step 4, the droplet generation stage, the decrease in fluid surface tension due to temperature rise is compensated by adjusting the turn-off phase of the initial bias voltage. In step 5, closed-loop feedback regulation, the system uses captured residual vibration data to verify the effect of temperature compensation. If the actual residual vibration frequency is higher than the expected frequency after compensation, the system updates the coefficients of the compensation table using a recursive least squares algorithm, achieving self-evolution of control parameters. This dual-modal closed-loop control architecture ensures that the printing system has strong resistance to external environmental disturbances during 24 / 7 operation in an industrial workshop.

[0073] Example 7

[0074] See Figures 1-5 This embodiment details an implementation scheme for improving the jet frequency limit. In step 1, the reinforcing rib structure of the flexible vibrating diaphragm is made of a composite material with high internal damping characteristics, embedded between silicon nitride layers through a stepwise deposition process. This design can significantly accelerate the attenuation of high-frequency vibrations without reducing static stiffness.

[0075] In the controlled energy storage step 2, the boost slope is increased to its critical stability upper limit of 8V / μs to compress the time of a single injection cycle. Through high-frequency capacitor monitoring (30MHz), the system immediately enters standby mode the instant the diaphragm reaches the target position. In the ultrafast triggering step 3, two sets of parallel discharge circuits operate alternately to reduce heat accumulation in the power devices, ensuring the turn-off time remains stable at 3 microseconds.

[0076] In step 5, closed-loop feedback regulation, active vibration damping logic is introduced. After the shock wave generated by the diaphragm rebound completes droplet ejection, the system immediately applies a phase-corrected reverse braking pulse based on the first oscillation peak captured by capacitive feedback. The electrostatic attraction generated by this pulse is opposite to the direction of diaphragm movement, instantly canceling the remaining kinetic energy of the diaphragm and rapidly returning it to a stationary state. Through this active damping control, the total duration of a single ejection cycle is reduced by 60%, thereby increasing the system's maximum continuous ejection frequency from the traditional 1kHz to 5kHz, significantly improving the production efficiency of high-viscosity printing.

[0077] Example 8

[0078] See Figures 1-5This embodiment relates to the implementation details of multi-material mixing printing. In step 1, an actuator structure is constructed having multiple microfluidic chambers arranged in parallel and converging into a single mixing nozzle. Each microfluidic chamber is covered with an independent flexible vibrating diaphragm.

[0079] In step 2, to accommodate the viscosity differences between the components (component A is 80 cP, component B is 200 cP), the system sets different controlled pressure ramps for the two channels. Capacitive feedback independently locks the pre-deformation displacement of each channel to ensure accurate instantaneous mixing of the two materials within the mixing chamber.

[0080] In step 3, the system precisely controls the voltage turn-off time difference between the two channels. Through a microsecond-level phase difference, the shock waves generated by the two components undergo nonlinear superposition at the convergence point. In step 4, the synthesized composite shock wave drives the mixed fluid to be ejected. In step 5, the residual vibration data from the capacitance feedback of each channel is used to evaluate the damping characteristics of the mixed fluid in real time. If the viscosity of the mixture exceeds a preset range, the system will immediately provide feedback and adjust the pre-deformation displacement of each channel in the next cycle, thereby achieving closed-loop digital control of the complex multi-component fluid printing process.

[0081] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for generating nanoscale droplets by impact printing based on microelectromechanical systems, characterized in that, Includes the following steps: Step 1, Constructing the actuator: The actuator structure is fabricated using micromachining technology. The actuator structure includes a microfluidic cavity disposed on a substrate, a nozzle connected to the bottom of the microfluidic cavity, and a flexible vibrating membrane that seals and covers the top of the microfluidic cavity. The surface of the flexible vibrating membrane is provided with reinforcing ribs to improve the rigidity of the structure. The flexible vibrating membrane is arranged in parallel with the fixed electrostatic driving electrode as a movable electrode to form a capacitive driving unit with an initial gap. Step 2, Controlled Energy Storage: An initial bias voltage with a controlled ramp rate is applied to the electrostatic driving electrode. The generated electrostatic attraction drives the flexible vibrating membrane to undergo slow elastic deformation in a direction away from the bottom of the microfluidic cavity. The real-time capacitance value between the flexible vibrating membrane and the electrostatic driving electrode is collected in real time using a capacitance monitoring link. The pre-deformation displacement of the flexible vibrating membrane is locked based on the change trajectory of the real-time capacitance value. Step 3, Ultra-fast triggering: At the predetermined injection triggering moment, the initial bias voltage is turned off within a preset time constant by the fast discharge circuit, releasing the electrostatic drive electrode from the flexible vibrating diaphragm. The flexible vibrating diaphragm rebounds towards the interior of the micro-liquid cavity with an instantaneous acceleration of not less than 1.2×10^5m / s² under the drive of its stored elastic restoring force, thereby generating a high-energy shock wave in the micro-liquid cavity. Step 4, droplet generation: The high-energy shock wave drives the fluid in the microfluidic cavity to overcome surface tension and viscous resistance, and ejects it outward from the nozzle to form droplets on the order of 5pL to 20pL. Step 5, Closed-loop feedback adjustment: The residual vibration data of the flexible diaphragm after rebound is captured using the real-time capacitance value, and the damping ratio in the residual vibration data is analyzed. Change According to the formula Calculate the required voltage compensation amount ,in The compensation coefficient is preset, and the compensation amount is verified and fine-tuned based on the pre-stored three-dimensional compensation lookup table of "residual vibration frequency-viscosity-bias voltage", thereby dynamically adjusting the control parameters of the initial bias voltage in subsequent injection cycles.

2. The method for generating nanoscale droplets by impact printing based on microelectromechanical systems according to claim 1, characterized in that, In step one, the microfluidic cavity of the actuator is formed on a single-crystal silicon substrate using deep reactive ion etching (DRIE). The geometric contour of the microfluidic cavity is defined on the surface of the single-crystal silicon wafer using photolithography, followed by vertical downward extension using high-selectivity plasma dry etching to form a cavity structure with vertical sidewalls. The depth of the microfluidic cavity is controlled within a preset depth range, and its bottom geometry is optimized to reduce dead zones for fluid flow. The nozzle is located at the center of the bottom of the microfluidic cavity and is formed using laser drilling or DIE. The inner diameter of the nozzle is set within a preset aperture range based on the target droplet volume. The flexible vibrating diaphragm is made of low-stress silicon nitride material and prepared using plasma-enhanced chemical vapor deposition (PECVD). During the preparation process, [the following steps are taken]. The residual stress of the flexible diaphragm is controlled within a preset tensile stress state by adjusting the flow ratio of ammonia to silane and the radio frequency power, ensuring its flatness after multiple reciprocating motions. The thickness of the flexible diaphragm is set within a preset thickness range, and its mechanical strength is improved by the reinforcing rib structure distributed on the surface. The reinforcing rib structure is radially and uniformly distributed on the surface of the flexible diaphragm, and it is integrally formed with the flexible diaphragm body through a stepwise chemical vapor deposition process. The flexible diaphragm serves as a movable electrode, and its surface is covered with a metal conductive layer of a preset thickness by a sputtering process. The fixed electrostatic driving electrode is disposed above the flexible diaphragm, and the two are maintained with a preset initial gap through a sacrificial layer or micro-machining pillars, forming the capacitive driving unit.

3. The method for generating nanoscale droplets by impact printing based on microelectromechanical systems according to claim 1, characterized in that, In step two, the specific value of the controlled pressure ramp is set to ensure that the rising speed of the flexible vibrating membrane is always lower than the critical value of the fluid replenishment speed in the microfluidic cavity. By controlling the pressure ramp within a preset rate of change threshold, sufficient replenishment time is given to the fluid, preventing cavitation bubbles from being triggered by a sudden drop in pressure inside the microfluidic cavity due to the excessively fast lifting speed of the flexible vibrating membrane, thereby ensuring that the microfluidic cavity is in a fully filled state during the energy storage stage. During the voltage boosting process, the system uses a high-precision capacitance detection chip integrated in the drive circuit to monitor the real-time capacitance value between the flexible diaphragm and the electrostatic drive electrode at a preset sampling frequency. The capacitance detection chip has a preset displacement measurement resolution, and by monitoring the change trajectory of the capacitance value, it inverts the spatial position of the flexible diaphragm. When the real-time capacitance value reaches the target capacitance value corresponding to the target displacement, the drive circuit automatically enters the voltage holding mode to lock the pre-deformation displacement of the flexible diaphragm.

4. The method for generating nanoscale droplets by impact printing based on microelectromechanical systems according to claim 1, characterized in that, In step three, the initial bias voltage is turned off through a fast discharge circuit connected in parallel across the electrostatic drive electrode. The fast discharge circuit includes a fast discharge power device with a preset low equivalent series resistance and parasitic inductance, capable of releasing the charge accumulated on the electrode surface within a preset time threshold. At the instant the flexible vibrating diaphragm is released from its electrostatic constraint, its stored elastic potential energy is completely released, generating an instantaneous acceleration of 1.2 × 10⁵ m / s² or higher, rebounding towards the microfluidic cavity. The generated high-energy shock wave is formed by the impact force applied to the fluid by the flexible vibrating diaphragm during its rebound. The magnitude of this impact force is determined by the effective mass of the flexible vibrating diaphragm, its instantaneous acceleration, the equivalent stiffness coefficient of the flexible vibrating diaphragm, and its pre-deformation displacement. The high-energy shock wave has a steep pressure wave front, generating instantaneous pressure that reaches a preset pressure peak, which is sufficient to shear the liquid bridge of the material within a preset viscosity range, counteract the intermolecular viscous force inside the fluid, and cause the fluid to break instantaneously at the nozzle outlet.

5. The method for generating nanoscale droplets by impact printing based on microelectromechanical systems according to claim 1, characterized in that, In step four, the inner wall and outlet end face of the nozzle are coated with an anti-fouling coating of a preset thickness. The anti-fouling coating works synergistically with the high-acceleration rebound of the flexible vibrating diaphragm. When the high-energy shock wave reaches the nozzle, the fluid gains outward momentum and, due to the extremely high strain rate, exhibits shear-thinning characteristics, reducing jet resistance. By adjusting the phase relationship between the turn-off time of the initial bias voltage and the capacitor sampling clock through the control system, the volume of a single droplet is finely adjusted, keeping the droplet volume precisely controlled within a predetermined micro-level and eliminating parasitic satellite droplets behind the main droplet. When processing bio-ink containing living cells, the duration of the high-energy shock wave is controlled within a preset duration threshold to ensure that the instantaneous shear force acting on the cell membrane is below the damage threshold, maintaining a predetermined cell viability rate.

6. The method for generating nanoscale droplets by impact printing based on microelectromechanical systems according to claim 1, characterized in that, In step five, the residual vibration data includes the oscillation frequency, damping ratio, and equilibrium position offset of the flexible diaphragm after spraying; the digital signal processing unit inside the control system performs fast Fourier transform processing on the acquired capacitance signal to extract the characteristic frequency characterizing the fluid viscosity fluctuation. If the amplitude of the rebound residual vibration of the flexible diaphragm exceeds a preset threshold, the system will apply a reverse pulse voltage with opposite phase during the first oscillation cycle after the voltage is turned off. This will utilize reverse electrostatic attraction to achieve active vibration reduction, thereby shortening the system preparation time and increasing the maximum continuous injection frequency. The control system will automatically adjust the amplitude of the initial bias voltage or the controlled boost slope for the next injection cycle based on the feedback results to offset the energy deviation caused by changes in the fluid physical properties due to environmental factors, and maintain the consistency of droplet volume during long-term operation.

7. The method for generating nanoscale droplets by impact printing based on microelectromechanical systems according to claim 1, characterized in that, In step two, the real-time capacitance value locking mechanism continuously compares the current capacitance value with the set target value through a comparator circuit. When the flexible diaphragm is stretched upward to the predetermined position corresponding to the target capacitance value, the drive circuit automatically enters the voltage holding mode to lock the pre-deformation displacement of the flexible diaphragm. Through pre-deformation displacement control based on capacitance feedback, the mechanical fatigue effect caused by the increase of the driver material with the increase of the usage time is eliminated, ensuring that after a predetermined number of spray cycles, the displacement accuracy deviation of the flexible diaphragm is still within the preset allowable deviation range. Moreover, the capacitance monitoring link suppresses common-mode noise through a differential detection circuit, ensuring the sensing accuracy of the position of the flexible diaphragm at sub-micron displacement.

8. The method for generating nanoscale droplets by impact printing based on microelectromechanical systems according to claim 1, characterized in that, The method achieves large-scale integrated printing through a multi-channel parallel control architecture. Each jetting unit has an independent capacitance monitoring link and performs individualized compensation for differences in fluid supply velocity at different physical locations. Upon receiving a global trigger signal, each channel fine-tunes the discharge delay based on the real-time capacitance value at that moment. By performing phase compensation on the discharge moment within a sub-microsecond timescale, the pressure wave leading edge generated by each channel is ensured to be synchronized. Each jetting unit is supplied with an initial bias voltage in parallel by an independent digital-to-analog converter. By analyzing the residual vibration data of each channel in real time, a viscosity distribution heatmap of the entire array is established. If a local viscosity change is detected in a specific area of ​​the array, the system automatically adjusts the driving parameters of the targeted jetting unit. When the capacitance signal fluctuates significantly due to external electromagnetic interference, the system automatically switches to the piezoresistive strain signal integrated at the edge of the flexible vibrating membrane for displacement calibration and adjustment.

9. The method for generating nanoscale droplets by impact printing based on microelectromechanical systems according to claim 1, characterized in that, In step one, the sidewall of the microfluidic cavity is provided with a functional layer with gradient wettability. The end of the functional layer near the flexible vibrating membrane is oleophilic, and the end near the nozzle is oleophobic. This gradient wettability structure, in conjunction with the directional shock wave generated by the flexible vibrating membrane, induces the fluid to converge towards the central axis of the nozzle, reducing energy dissipation on the sidewall. The reinforcing rib structure adopts a high-density grid distribution, and its material is high-modulus silicon carbide. It is integrally formed with the flexible vibrating membrane body through a low-pressure chemical vapor deposition process, which improves the equivalent stiffness coefficient of the flexible vibrating membrane to withstand electrostatic attraction under extremely high pressure and maintain non-plastic deformation. The reinforcing rib structure can suppress the higher-order vibration modes of the flexible vibrating membrane during high-speed rebound, ensuring that energy is concentrated in the main vibration direction and improving the transmission efficiency of pressure waves.

10. The method for generating nanoscale droplets by impact printing based on microelectromechanical systems according to claim 1, characterized in that, In step two, the initial bias voltage amplitude is nonlinearly mapped and adjusted according to the real-time viscosity of the fluid to be printed. The control system determines the elastic prestress level for different material properties by querying a three-dimensional compensation table containing temperature, viscosity, and driving voltage pre-stored in the memory in real time, thus achieving compatibility with fluid materials with different filling rates. In step five, the closed-loop feedback regulation also includes using a digital signal processing unit to monitor the zero-point offset state of the flexible vibrating membrane after rebound in real time, and evaluating the liquid residue at the nozzle outlet based on the zero-point offset state. If the liquid residue exceeds a preset fluctuation threshold, a high-frequency micro-amplitude oscillation voltage is applied to the electrostatic drive electrode in the next non-jetting cycle to achieve self-cleaning of the nozzle through micro-mechanical vibration. The system uses the captured residual vibration data to verify the compensation effect and updates the compensation parameters through a recursive algorithm to achieve self-evolution of the control parameters.

Images