I. Abstract of the Paper’s Core Research

This study employs aerosol jet deposition to fabricate multilayer PZT dual‑piezoelectric push–pull actuators on a 301 stainless steel substrate, and integrates these with a gradient‑etched single‑mode scanning optical fiber to construct a mirrorless fiber‑MEMS imaging‑scanning system. Device scanning performance is validated through finite element simulations, laser Doppler vibrometry, and microscopic imaging. The work provides a comprehensive analysis of aerosol‑based piezoelectric layer fabrication, fiber modification, and the nonlinear two‑dimensional scanning mechanism. The key findings are as follows:

Aerosol Room-Temperature Deposition of Thick-Film PZT Piezoelectric actuator

Without the need for high‑temperature vacuum sputtering, a 5‑μm‑thick, uniform PZT thin film is directly deposited via room‑temperature aerosol printing, followed by photolithographic patterning and lift‑off to form four piezoelectric push–pull electrodes. After annealing at 520°C and poling, the material exhibits a dielectric constant of 1276, with piezoelectric performance comparable to that of vacuum‑deposited films. Moreover, the stainless‑steel substrate offers significantly superior mechanical toughness compared to silicon wafers, substantially reducing the likelihood of fracture‑induced failure.

One-dimensional drive nonlinear two-dimensional spiral scanning mechanism

Under single‑channel triangular‑wave excitation, the fiber’s asymmetric structure induces nonlinear vibrations, autonomously generating circular and helical scanning trajectories. A single set of drive signals suffices to achieve X/Y dual‑axis scanning, eliminating the need for a dual‑channel phase‑synchronization control circuit and significantly reducing system‑control costs. With a 8005 Hz fundamental frequency paired with 10 Hz amplitude modulation, it can stably produce a helical scan region 60 μm in diameter at a frame rate of 10 fps.

Quasi-Static Graded-Etch Fiber Optimizes Optical Scanning Performance

An innovative segmented‑lift HF etching process was developed to fabricate long, gradient‑index fiber tapers. Compared with static etching, this approach increases the end‑point displacement by a factor of ten, achieving a maximum lateral displacement of 110 μm and a longitudinal displacement of 500 μm at a high frequency of 8 kHz. After beam focusing, the imaging resolution can reach a line width of 5 μm.

Low-Cost Additive Manufacturing Process for the Entire Workflow

A stainless steel substrate replaces costly SOI wafers; an aerosol‑free, maskless direct‑printing process is used to pattern the piezoelectric layer, requiring only a single photolithography step, which significantly reduces the number of MEMS microfabrication steps. The device’s overall footprint is just 17 × 10 mm.

Experimental validation of multi-scenario imaging

Scanning imaging has been successfully performed on a 5-μm standard grating, a 15-μm cross‑shaped mask, and the microstructures of insect wings. Image distortion can be corrected via software algorithms, making the system suitable for minimally invasive endoscopy and ex vivo biological microscopy.

II. Complete Fabrication Process of Aerosol‑Based PZT‑MEMS Scanning Devices

Substrate Pre-treatment: 60 μm 301 stainless steel foil, cleaned with a piranha solution; double-sided spin-coated negative photoresist used for aerosol‑based patterning.

Aerosol喷射 PZT piezoelectric layer: Pneumatic atomization is used to prepare a PZT ceramic slurry, which is then deposited layer by layer to form 5-μm-thick piezoelectric films. The films are subsequently delaminated using acetone to obtain a four‑zone push–pull electrode pattern.

Electron-beam evaporation of Ti/Pt electrodes on both sides, followed by another photolithography and lift-off process to define the conductive leads.

A hydrochloric–nitric acid etching process on a stainless steel substrate releases a cantilevered push-pull frame.

520℃ stepwise annealing , Polarization at 180°C activates the piezoelectric properties;

Quasi‑static etching of a single‑mode optical fiber using an HF/toluene mixed solution in segmented steps to fabricate a gradient‑tapered scanning fiber.

Epoxy adhesive secures the optical fiber at the center of the MEMS cantilever, and a GRIN gradient lens is assembled to complete the imaging module.

Vibration modal testing, laser scanning imaging, and scanning characterization of biological samples.

III. Five Core Process Advantages of PZT Actuators for Aerosol Preparation (Vacuum Sputtering / (Sol–gel comparison)

Room-temperature, vacuum-free deposition significantly lowers the equipment barrier.

No high-vacuum deposition chamber is required; aerosol-based, atmospheric-pressure direct printing of piezoelectric thick films enables rapid prototyping in small and medium-sized laboratories, significantly reducing costs.

Adaptation to stainless steel flexible substrates addresses the issue of easy cracking in silicon-based piezoelectrics.

301 stainless steel has a modulus of elasticity that is better suited to reciprocating vibrations, making it less prone to fracture under long-term high-frequency scanning and thereby extending the device’s service life.

Maskless digital patterning, with on-demand customization of piezoelectric partitioned push-pull structures.

CAD‑based customization of a four‑electrode array eliminates the need for a custom silicon etching mask, thereby shortening the iteration cycle for different actuator designs.

The thick film is precisely controllable, with the piezoelectric layer uniformly formed at 5 μm.

The single‑layer deposition thickness is stable, with no pinholes or non‑uniformity in film thickness, and the piezoelectric response exhibits high consistency after annealing.

Compatible with large-area stainless steel substrates, supporting the batch fabrication of array‑type MEMS scanning chips.

6-inch stainless steel monolithic batch‑printed multi‑actuator arrays, ideal for small‑scale mass production of medical imaging devices.

IV. Five Core Technological Innovations of This Study

Innovation 1: A novel aerosol direct‑printing stainless‑steel‑based PZT push–pull actuator design

Aerosol jetting is employed in the fabrication of fiber‑optic MEMS piezoelectric actuators, circumventing the costly process constraints of silicon‑based microfabrication.

Innovation 2: Single-Channel Excitation Nonlinear Two-Dimensional Scanning Mechanism

By leveraging the nonlinear resonance induced by asymmetric deformation of an optical fiber, a single‑channel signal enables helical dual‑axis scanning, eliminating the need for dual‑channel phase‑driven hardware.

Innovative 3‑step quasi‑static segmented etching technique for fabricating graded-index optical fibers

It addresses the pain points of fragile, easily fractured static-etching fiber tips and insufficient displacement, significantly enhancing the scanning field of view and imaging resolution.

Innovative 4‑V Low‑Voltage Miniature MEMS Imaging Integrated Architecture

It operates with a drive voltage of only ±10 V, eliminating the need for high‑voltage electrostatic structures exceeding hundreds of volts, and is compatible with portable, minimally invasive micro‑imaging probes.

Innovation 5: Simplifying the MEMS Microfabrication Additive Manufacturing Paradigm

Piezoelectric-layer aerosol direct printing replaces multi‑channel vacuum deposition, cutting the lithography process in half and boosting the R&D efficiency of micro‑scanning devices.

V. Current Industry Challenges and Corresponding Solutions

Challenge 1: Traditional silicon-based MEMS galvanometers are highly brittle, prone to fracture under high-frequency vibration, and feature complex packaging.

✅ Stainless steel flexible substrate + room-temperature piezoelectric thin film in an aerosol chamber, offering fatigue‑resistant vibration performance and enhanced device reliability.

Challenge 2: Dual-axis scanning requires two sets of drivers and dual-channel phase circuits, making the control system more complex.

✅ Nonlinear resonant single‑channel drive, using only one signal generator, thereby reducing the overall hardware cost.

Challenge 3: Vacuum sputtering PZT equipment is expensive, while the sol–gel method yields thin films with weak piezoelectric properties.

✅ Aerosol deposition enables the direct formation of micrometer-thick piezoelectric layers, resulting in stronger piezoelectric strain output and lower equipment costs.

Challenge 4: Conventional etching produces short fiber tapers, small scanning displacements, and a narrow imaging field of view.

✅ Quasi‑static segmented pull‑etching, with long‑gradient fibers that significantly broaden the tip’s vibration range.

Challenge 5: Traditional MEMS devices involve numerous lithography and deposition steps, resulting in long prototyping lead times.

✅ Aerosol-based maskless direct printing of piezoelectric functional layers, significantly reducing complex wafer-level microfabrication steps.

VI. Future Diversified Industrial Application Scenarios

1 Minimally Invasive Medical Endoscopic Imaging Probe

Ultra‑fine fiber‑optic scanning module, a miniature imaging unit for gastrointestinal and ENT minimally invasive endoscopes, with no bulky galvanometer.

2 In vitro biological microscopy equipment

Rapid scanning imaging of cellular and insect tissue microstructures, with a low-cost miniature confocal auxiliary light source for laboratory use.

3 Portable Miniature Spectral Scanning Instrument

Miniaturized optical scanning module, a core component of handheld environmental monitoring and compact fluorescence analysis instruments.

4 Consumer-grade miniature laser projection module

Low-voltage compact helical-scanning fiber, lightweight miniature projection optical engine.

5 MEMS Optical Device Laboratory High-Throughput R&D Platform

Aerosol-based rapid printing of PZT actuators in various sizes enables batch testing of scanning performance, thereby shortening the iteration cycle.

Image and Text Guide

Figure 1. “Push–pull” MEMS scanner employing an aerosol‑jet‑printed (AD) PZT bimorph actuator and a tapered optical fiber: concept, design, fabrication process, and final device.

Figure 2. Finite element (FEA, ANSYS APDL) model of the scanner, two-dimensional modal motion under one-dimensional excitation, and simulated displacement at the fiber tip.

Table 1. Modal Analysis Results: First 23 Natural Frequencies of the Full System, Actuators, and Static-Etched vs. Quasi-Static-Etched Optical Fibers

Figure 4. Comparison of the fiber tapering process with static and quasi-static etching results.

Figure 5. Experimental setup for scanner illumination and control testing

Figure 6. Scanner motion patterns: one-dimensional scanning, Lissajous figures, frequency response, single-frequency nonlinear two-dimensional scanning, and spiral scanning.

Figure 7. Reconstruction results: chromium mask pattern and imaging of a moth fly (Psychodidae) wing.

Figure 8. Frame Isolation in Helical Scanning and Image Reconstruction