Fabrication of a high aspect ratio thick silicon wafer mold and electroplating using flipchip bonding for MEMS applications

Kim, Bong-Hwan; Kim, Jong-Bok

doi:10.1088/0960-1317/19/6/065024

Cited by 11 publications

(9 citation statements)

References 28 publications

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“…Development of the vertical walls for return electrodes is far from trivial: with the wall height of 25 µm (set by the thickness of INL) and its ideal width of 2 µm for 20 µm pixels, the aspect ratio exceeds a factor of 12. Conventional lithography struggles to provide such a high aspect ratio [50,51], and we are evaluating various options. Meanwhile, we started the assessment of the smaller pixels and the associated retinal stimulation threshold in a monopolar flat configuration of the array since it generates electric nearfield similar to that expected with honeycombs: under full-field illumination: the field is oriented vertically within the retinal thickness and is independent of pixel size, as shown in Figure 9f.…”

Section: Discussionmentioning

confidence: 99%

Vertical-junction Photodiodes for Smaller Pixels in Retinal Prostheses

Huang

Kamins

Chen

et al. 2020

Preprint

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Objective: To restore central vision in patients with atrophic age-related macular degeneration, we replace the lost photoreceptors with photovoltaic pixels, which convert light into current and stimulate the secondary retinal neurons. Clinical trials of this technology demonstrated shaped vision with prosthetic acuity closely matching the sampling limit of the 100 μm pixels. Reduced pixel size may improve visual acuity, but with smaller flat bipolar pixels, penetration depth of electric field and diode photoresponsivity significantly decrease, making the device ineffective. Smaller pixels may be enabled by shaping the electric field vertically using 3-D electrodes and by increasing the diode responsivity using vertical p-n junctions. Approach: Arrays of silicon photodiodes of 55, 40, 30, and 20 μm in width, having vertical p-n junctions, were fabricated. Electric field in the retina was shaped vertically by a common return electrode at the edge of the 1.5 mm wide devices. Optical and electronic performance of the diodes was characterized in-vitro, and retinal stimulation threshold measured by recording visually evoked potentials (VEPs) in rats with retinal degeneration. Main results: The photodiodes exhibited sufficiently low dark current (<10 pA) and responsivity at 880 nm wavelength as high as 0.51 A/W, with 85% internal quantum efficiency, independent of pixel size. Field mapping in saline demonstrated uniformity of the pixel performance in the array. The full-field stimulation threshold was as low as 0.057±0.029 mW/mm2 with 10 ms pulses, independent of pixel size. Significance: Photodiodes with vertical p-n junctions demonstrate excellent charge collection efficiency independent of pixel size, down to 20 μm. Vertically oriented electric field provides a stimulation threshold independent of pixel size. These results are a first step in validation of the concept of the field shaping with 3-D electrodes for subretinal stimulation.

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Section: Discussionmentioning

confidence: 99%

Vertical-junction Photodiodes for Smaller Pixels in Retinal Prostheses

Huang

Kamins

Chen

et al. 2020

Preprint

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“…Through the advanced manufacturing process combining microelectronics and micro-machining, various micro-systems with excellent performance, miniaturization and highly integrated sensors and actuators can be prepared. It was more and more widely applied in the fields of national defense, military, information, Internet of Things, biology, medicine, automobile, wearable consumer electronics, and so on [1][2][3][4]. Polydimethylsiloxane (PDMS) microfluidic chips have been widely used for MEMS because of good biocompatibility, low optical transparency and non-toxicity.…”

Section: Introductionmentioning

confidence: 99%

Study on ablation properties of PDMS by 193 nm and 248 nm excimer laser

Zhang¹,

Zhang²,

Li³

et al. 2023

International Conference on Optoelectronic Materials and Devices (ICOMD 2022)

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Laser direct writing technology was a convenient and efficient method in micromachining, which was widely used in polymer processing. In this paper, two kinds of excimer laser (193 nm and 248 nm) were used to irradiate vertically the surface of polydimethylsiloxane (PDMS) for ablation experiments. The experiments were carried out in atmospheric environment, and the ablated samples were characterized by optical microscope, laser confocal microscope, white light interferometer, scanning electron microscope, etc. to obtain their morphology. Analysis was performed on the effects of laser energy and pulse numbers on depth, roughness, and morphology. The outcomes demonstrated that, the crater depth and roughness increased as the number of pulses and energy increased, but that the bottom surface's roughness did not continuously increased with the ablation of a 248 nm laser. At low energy, the roughness remained constant as the number of pulses increased. When the laser operating voltage was adjusted to 23 kV, the roughness increased linearly with the number of pulses. As the laser energy and the number of pulses increased, the number of splashes deposited on the ablation surface increased. Cracks were generally observed across the PDMS surface after a 248 nm laser and the crater edges were rough. The morphology in the 193nm laser ablation showed better micromachining quality, reflected in a small number of pores, sharp edges, and smoother bottom surface.

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“…As a result of the high strength material property, the device can stay intact under a high impact, which can greatly improve the safety of the weapon system [7,8]. Unfortunately, the LIGA process is costly, and confined by the low resolution of the thick photoresist, the fabrication precision is not satisfactory [13]. In the silicon-based device, the structure is usually achieved by micromachining, which gives the device the features of high-precision and -integration [14,15,16].…”

Section: Introductionmentioning

confidence: 99%

The Hybrid Fabrication Process of Metal/Silicon Composite Structure for MEMS S&A Device

Fang

Zhang

et al. 2019

Micromachines

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The micro-electromechanical system (MEMS) safety-and-arming (S&A) device has the features of integration and miniaturization, which is one of the important directions of weapon development. Confined by the fabrication process, the silicon-based devices are too fragile, and the metal-based devices are low precision. In order to solve the contradiction between high precision and high structure strength, a metal/silicon composite structure is proposed in this paper, and a hybrid fabrication process is introduced. This new method mainly consists of metal sputtering, electroplating, and (inductively–coupled-plasma) ICP etching. As the resolution of the thick dry film is limited, the process of a femtosecond laser is applied to refine the structure, and the Ni plate (a block of 1 mm × 3 mm × 0.3 mm with a cavity of ϕ 0.85 mm × 0.3 mm in the center) is fabricated on the silicon-on-insulator (SOI) wafer successfully. After the double sides are etched by ICP, the SOI wafer is immersed in a buffered-oxide-etch (BOE) etchant to remove the buried layer. The cover plate acts as the encapsulation and is bonded with the SOI wafer by the epoxy glue. Then, the temporary support beam of the device is broken by the probe, and the suspended composite structure can be fully released. The hybrid process is the integration of the silicon-based process and the metal-based process, which can combine the advantages of both high precision and a high structure strength. The process proposed here is suitable for the application of weapon miniaturization.

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Fabrication of a high aspect ratio thick silicon wafer mold and electroplating using flipchip bonding for MEMS applications

Cited by 11 publications

References 28 publications

Vertical-junction Photodiodes for Smaller Pixels in Retinal Prostheses

Vertical-junction Photodiodes for Smaller Pixels in Retinal Prostheses

Study on ablation properties of PDMS by 193 nm and 248 nm excimer laser

The Hybrid Fabrication Process of Metal/Silicon Composite Structure for MEMS S&A Device

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