Aerosol Jet Printing (AJP) is an emerging contactless direct write approach aimed at the production of fine features on a wide range of substrates. Originally developed for the manufacture of electronic circuitry, the technology has been explored for a range of applications, including, active and passive electronic components, actuators, sensors, as well as a variety of selective chemical and biological responses. Freeform deposition, coupled with a relatively large stand-off distance, is enabling researchers to produce devices with increased geometric complexity compared to conventional manufacturing or more commonly used direct write approaches. Wide material compatibility, high resolution and independence of orientation have provided novelty in a number of applications when AJP is conducted as a digitally driven approach for integrated manufacture. This overview of the technology will summarise the underlying principles of AJP, review applications of the technology and discuss the hurdles to more widespread industry adoption. Finally, this paper will hypothesise where gains may be realised through this assistive manufacturing process.

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A review of aerosol jet printing—a non-traditional hybrid process for micro-manufacturing

In this paper, we demonstrate a passive wireless surface temperature sensor, based on a high-temperature co-fired ceramic process and a thick-film technology, which is functional up to 1400 °C. In addition, we propose a temperature measurement technique that makes use of the absolute amplitude of the S11 parameter. The sensor comprises an inductor (created from platinum) deposited on a ceramic substrate (99% alumina), making it cheap and easy to fabricate using a screen-printing technology, due to its simple structure. The use of temperature resistant materials, and a completely passive structure, means that this sensor is robust to harsh environments. The device operates using the principle of $LC$ resonance, illustrated in this paper with a lumped circuit model. The dielectric constant of the substrate increases with increasing temperature, leading to a monotonic variation in the resonant frequency of the sensor, which is retrieved wirelessly via a readout antenna. We set the test distance between the sensor and the antenna to 10 mm and observed a repeatable response between 26 °C and 1400 °C. S11 amplitude and resonant frequency are used to reflect the change temperature, respectively. And we found that it is more accurate to test the temperature by resonant frequency after comparing the experimental results. The average sensitivity of temperature test by resonance frequency is obtained, which is 14.3 kHz/°C.

A Novel Surface $LC$ Wireless Passive Temperature Sensor Applied in Ultra-High Temperature Measurement

This paper presents a kind of passive wireless pressure sensor comprised of a planar spiral inductor and a cavity parallel plate capacitor fabricated through low-temperature co-fired ceramic (LTCC) technology. The LTCC material with a low Young’s modulus of ~65 GPa prepared by our laboratory was used to obtain high sensitivity. A three-step lamination process was applied to construct a high quality cavity structure without using any sacrificial materials. The effects of the thickness of the sensing membranes on the sensitivity and detection range of the pressure sensors were investigated. The sensor with a 148 μm sensing membrane showed the highest sensitivity of 3.76 kHz/kPa, and the sensor with a 432 μm sensing membrane presented a high detection limit of 2660 kPa. The tunable sensitivity and detection limit of the wireless pressure sensors can meet the requirements of different scenes.

Fabrications and Performance of Wireless LC Pressure Sensors through LTCC Technology

There is an increasing demand for bearing temperature and strain monitoring in high-speed rotating systems. This study proposes a new multiresonance, multiplexing, wireless, passive inductance capacitance (LC) temperature and strain sensor. The sensor has two capacitors connected at different locations (turns) on the same inductor to achieve simultaneous temperature and strain measurements. The plate capacitor is connected to the inner part of the inductor and the other interdigital capacitor is connected to the outer part of the inductor to form two LC loops. The structure of the sensor is optimized through High Frequency Structure Simulator (HFSS) simulations to realize frequency separation of the two parameters and avoid mutual interference between the two signals. The sensor is fabricated on a polyimide film using electroplating technology. The experimental results show that the temperature–strain sensor can operate stably from 25 °C to 85 °C with an average sensitivity of 27.3 kHz/°C within this temperature range. The sensor can detect strains in the range of 1000–5000 μe with a strain sensitivity of 100 Hz/μe at 25 °C. Therefore, the proposed wireless passive LC temperature-strain sensor exhibits stable performance. In addition, the use of a single inductor effectively reduces the sensor’s area. The flexible substrate provides advantageous surface conformal attachment characteristics suitable for monitoring high-temperature rotating parts in adverse environments.

Wireless Passive LC Temperature and Strain Dual-Parameter Sensor

Aerosol jet printing (AJP) is a complex process for additive electronics that is often unstable. To overcome this instability, observation while printing and control of the printing process using image-based monitoring is demonstrated. This monitoring is validated against images taken after the print and shown highly correlated and useful for the determination of printed linewidth. These images and the observed linewidth are used as input for closed-loop control of the printing process, with print speed changed in response to changes in the observed linewidth. Regression is used to relate these quantities and forms the basis of proportional and proportional integral control. Electrical test structures were printed with controlled and uncontrolled printing, and it was found that the control influenced their linewidth and electrical properties, giving improved uniformity in both size and electrical performance.

Image-Based Closed-Loop Control of Aerosol Jet Printing Using Classical Control Methods

The LC resonator-based passive pressure sensor attracts much attention because it does not need a power source or lead wires between the sensing element and the readout system. This paper presents the design and manufacturing of a passive pressure sensor that contains a variable capacitor and a copper-electroplated planar inductor. The sensor is fabricated using silicon bulk micro-machining, electroplating, and anodic bonding technology. The finite element method is used to model the deflection of the silicon diaphragm and extract the capacitance change corresponding to the applied pressure. Within the measurement range from 5 to 100 kPa, the sensitivity of the sensor is 0.052 MHz/kPa, the linearity is 2.79%, and the hysteresis error is 0.2%. Compared with the sensitivity at 27 °C, the drop of output performance is 3.53% at 140 °C.

https://www.mdpi.com/2072-666X/7/5/87/pdf

Design and Manufacturing of a Passive Pressure Sensor Based on LC Resonance.

In this paper, a novel method to achieve through-via interconnection using Aerosol Jet technology is proposed. Compared with the conventional MEMS through-via metallization e.g., coating with shadow mask or electroforming, the Aerosol process is (1) Adapt to extremely confined geometries of via, (2) Save material due to depositing on demand, (3) Allow to pattern the extraction electrode without mask. To demonstrate the method, printed Ag on doped silicon sintering from 200 to 500 °C is prepared and evaluated by testing which reveals a sufficient specific contact resistance. Besides, as the SEM cross sections show, metal layer is with good coverage for trapezium or even reverse trapezium via using the Aerosol Jet. However, the printed Ag is vulnerable to thermal shock and prone to crack after sintering. The corresponding cracks, resulting from residual tensile stress caused by the difference of thermal expansion coefficients, can be greatly eliminated by naturally cooling down.

Application of Aerosol Jet technology in through-via interconnection for MEMS wafer-level packaging

In MEMS device, heavily boron doped layers are widely used as structural layers. For the manufacture of the thick heavily boron doped layer (boron concentration ≥ 5×1019 cm-3), conventional two-step method exposes disadvantages of low efficiency and high energy consumption. Hence, multi-step method is introduced to improve the energy efficiency. In our study, simulation of diffusion in silicon is carried out to compare multi-step method with conventional method. The simulation reveals that multi-step method obtains more quantity of boron dopants and shows better potential to fabricate thick heavily boron doped layers, compared to conventional method within the same total diffusion time. As a typical application of the multi-step method, a butterfly-shape resonant is fabricated.

Simulation and Typical Application of Multi-Step Diffusion Method for MEMS Device Layers

In this paper, two aspects in the wet glass etching, the pre-annealing of the glass and the mask process, are taken into consideration to achieve the deep and defect-free wet etching of Pyrex glass. Compared with the conventional strategies, i.e., HF solution component and mask kinds, our experiment results prove the pre-annealing is another key role to obtain theoretical isotropy character in wet etching. Besides, the high temperature pre-annealing dramatically improves the structure profiles and reduces the notching defects. Additionally, a novel multilayer mask process is proposed. With 1.5μm PR/ 100nm Au/ 100 nm Au/ 20 nm Cr mask and > 450 °C pre-annealing, > 150 μm deep and non-pin-holes Pyrex glass structures are achieved and the roughness of etched surface is lower than 1 nm.

Strategies for Defect-Free and Deep Wet Etching of Pyrex 7740

Conference Name:15th Annual Conference and 4th International Conference of the Chinese Society of Micro-Nano Technology, CSMNT 2013. Conference Address: Tianjin, China. Time:November 3, 2013 - November 6, 2013.

Cheng Zheng

Papers

Design and Manufacturing of a Passive Pressure Sensor Based on LC Resonance.

Application of Aerosol Jet technology in through-via interconnection for MEMS wafer-level packaging

Simulation and Typical Application of Multi-Step Diffusion Method for MEMS Device Layers

Strategies for Defect-Free and Deep Wet Etching of Pyrex 7740

Vertically Aligned Carbon Nanotubes Transfer with Glass Frit