| 1. |
- Lu, Yu, et al.
(författare)
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Electroless deposition of high-uniformity nickel microbumps with ultrahigh resolution of 8 μm pitch for monolithic Micro-LED display
- 2024
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Ingår i: Materials Science in Semiconductor Processing. - 1369-8001. ; 175
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Tidskriftsartikel (refereegranskat)abstract
- Micro-light-emitting diode (Micro-LED) displays have attracted growing attention due to their unsurpassed properties that satisfy the requirements of reality/virtual reality (AR/VR) displays. A crucial procedure of monolithic integration technology in high-density microdisplays is the interconnection process, which is intimately associated with the quality of the display device. Microfluidic electroless interconnection (MELI), an innovative low-temperature and pressure-free chip-stacking approach that eliminates the warpage-induced issues and cracking damage of the chip caused by thermo-compression bonding (TCB), holds great promise as a technology for establishing interconnections between the CMOS driver and Micro-LED. However, the requirement for the consistency of the microbump arrays and the risk of creating bridges is significantly intensified with smaller gaps in stacked chips, which restricts the application range of MELI to high-density interconnects. This paper analyzes the feasibility of further lowering the stand-off height of stacked chips in ultrafine pitch interconnects by optimizing the bump preparation process. The plasma modification time and surfactant concentration during the bump preparation process have been investigated. The result indicated that microbump arrays with a uniformity of less than 3% could be successfully manufactured by employing a 7-min plasma treatment and incorporating optimal surfactants, which catalyzes the implementation of the subsequent vertical interconnection process and eventually enhances yields of Micro-LEDs.
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| 2. |
- Lu, Yu, et al.
(författare)
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Electroless deposition of nickel microbumps for fine-pith flip-chip bonding
- 2024
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Ingår i: Journal of Physics: Conference Series. - 1742-6588 .- 1742-6596. ; 2783:1
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Konferensbidrag (refereegranskat)abstract
- The reliability of micro-light-emitting diode (Micro-LED) is closely associated with the uniformity of microbumps arrays. With continual decreases in pixel pitch in recent years, it is a challenge to guarantee the uniformity of bump arrays. To satisfy current requirements for ultra-high-density interconnections, this study proposes an electroless plating method for fabricating highly uniform nickel microbumps. This technique differs from electroplating, in which the morphology and consistency of microbumps can be easily controlled. Furthermore, it is a high-selectivity and cost-effective method of microbumps fabrication that eliminates solder wastage and avoids metal lift-off in traditional evaporation. To minimize the non-uniformity of the bumps, we aim to optimize the oxygen plasma treatment parameters and deposition intervals to eliminate the issues of skip plating, hydrogen bubble entrapment, and nodules. Under the combined effect of plasma treatment and intermittent deposition method, microbump arrays with less than 5% uniformity were successfully prepared, achieving the demands of high-density bonding. In addition, the preparation process is highly reproducible, extending the application range of this technique.
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| 3. |
- Pan, Kui, et al.
(författare)
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Highly effective transfer of micro-LED pixels to the intermediate and rigid substrate with weak and tunable adhesion by thiol modification
- 2023
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 15:9, s. 4420-4428
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Tidskriftsartikel (refereegranskat)abstract
- Based on transfer printing technology, micro-LED pixels can be transferred to different types and sizes of driving substrates to realize displays with different application scenarios. To achieve a successful transfer, GaN-based micro-LEDs first need to be separated from the original epitaxial substrate. Here, micro-LED pixels (each size 25 μm × 30 μm) on the sapphire substrate were transferred to a flexible semiconductor wafer processing (SWP) tape that is strongly sticky by conventional laser lift-off (LLO) techniques. The pixels on the SWP tape were then transferred by using a sacrificial layer of non-crosslinked oligomeric polystyrene (PS) film onto the intermediate and rigid substrate (IRS) with weak and tunable adhesion by thiol (-SH) modification. The electrode of the micro-LED is Au metal, which forms Au-S bonds with the surface of the IRS to fix the pixels. The rigid substrate helps ensure that the pixel spacing is almost unchanged during the stamp transfer process, and the weak and tunable adhesion facilitates the pixels being picked up by the stamp. The experimental results demonstrate that the pixels can be efficiently transferred to the IRS by LLO and sacrificial layer-assistance, which will provide the possibility of achieving the further transfer of pixels to different types and sizes of driving substrates by a suitable transfer stamp. The transfer process details are discussed, which can provide insights into the transfer of micro-nano devices through polymer sacrificial layers.
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| 4. |
- Pan, Kui, et al.
(författare)
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Ultrasmall-sized light-emitting diodes fabricated by ion implantation based on GaN epitaxial wafers with fully activated or unactivated p-GaN
- 2024
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 49:17, s. 4835-4838
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Tidskriftsartikel (refereegranskat)abstract
- A key challenge in realizing ultrahigh-resolution displays is the efficient preparation of ultrasmall-sized (USS) light-emitting diodes (LEDs). Today, GaN-based LEDs are mainly prepared through dry etching processes. However, it is difficult to achieve efficient and controllable etching of USS LED with high aspect ratios, and LED sidewalls will appear after etching, which will have a negative impact on the device itself. Herein, a method for preparing USS LED based on GaN epitaxial wafers is reported (on two types of wafers, i.e., with p-GaN fully activated and unactivated). F−ions are injected into the intentionally exposed areas on the two types of wafers to achieve device isolation. The area under the micro-/nanosized protective masks (0.5, 0.8, 1, 3, 5, 7, 9, and 10 µm wide Ni/Au stripes) are the LED lighting areas. The LED on the p-GaN unactivated wafer (UAW) requires further activation. The Ni/Au mask not only serves as the p-electrode of LED but also Ni as a hydrogen (H) removing metal covering the surface of p-GaN UAW that can desorb H from a Mg element in the film at relatively low temperatures, thereby achieving the selective activation of LED lighting areas. Optoelectronic characterization shows that micro-/nano-sized LED arrays with individual-pixel control were successfully fabricated on the two types of wafers. It is expected that the demonstrated method will provide a new way toward realizing ultrahigh-resolution displays. Analyzing the changes in the current flowing through LED (before and after selective activation) on the F−injected p-GaN UAW, it is believed that depositing H removing metal on p-GaN UAW could possibly realize the device array through the selective activation only (i.e., without the need for ion implantation), offering a completely new insight.
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| 5. |
- Tian, Liang, et al.
(författare)
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Electroless Deposition of 4 μm High Ni/Au Bumps for 8 μm Pitch Interconnection
- 2022
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Ingår i: ACS Applied Electronic Materials. - : American Chemical Society (ACS). - 2637-6113. ; 4:10, s. 4966-4971
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Tidskriftsartikel (refereegranskat)abstract
- We propose that electroless plating is a superb approach to preparing metallic bumps with an ultrafine pitch for the integration of a micro light-emitting diode (micro-LED). Electroless plating does not suffer from lift-off-related issues, which are ubiquitous in thermal evaporation. Besides, it can result in much more uniform bumps than electroplating because the bump height is not affected by the current distribution. This study reports ultrafine pitch Ni/Au bumps fabricated by electroless nickel immersion gold (ENIG) plating. Furthermore, cheap metals iron and nickel are selected to catalyze the electroless nickel process. The results indicate that uniform and consistent Ni/Au bumps can be obtained through the iron sheet and nickel layer method. Besides, no voids and impurities are found inside the bumps, which is beneficial for the following interconnection process. Moreover, the change in Ni bump height values with the electroless plating time is also provided.
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| 6. |
- Wang, Shuaishuai, et al.
(författare)
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Fabrication of Super Uniform Nickel Bumps Using Electroless Plating on Micro-LEDs’ TFT Driver Substrates
- 2024
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Ingår i: Digest of Technical Papers - SID International Symposium. - 2168-0159 .- 0097-966X. ; 55:S1, s. 194-196
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Konferensbidrag (refereegranskat)abstract
- In this study, in order to achieve high-yield Micro-LED chip bonding and thus further advance the breakthrough of Micro- LED interconnect technology. In this study, an electroless plating method is used to achieve the highly uniform nickel bump arrays on thin film transistor (TFT) driver substrate. Initially, the photoresists AZ4620 and AZ2070 are chosen for the experiments, which can cover the step structure uniformly of TFT substrate. Subsequently, the morphology of bumps on the TFT substrate influenced by the plasma treatment and the deposition time is investigated. The 1% uniformity of the nickel bump arrays by the electroless plating for 30 minutes after 5-minute plasma treatment is achieved, which lays the foundation for the electroless plating self-bonding.
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| 7. |
- Zhu, Xuanyu, et al.
(författare)
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Liquid Phase Deposition of Hafnium Oxide Thin Films
- 2024
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Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - 1558-4135 .- 1070-9878. ; 31:4, s. 1659-1665
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Tidskriftsartikel (refereegranskat)abstract
- Hafnium oxide (HfO2) thin films were successfully prepared by the liquid phase deposition (LPD) method. The surface appearance, composition, optical characteristics, and electrical properties of HfO2 thin films generated by LPD were studied, as well as the reaction mechanism. The results reveal that the chemical composition of HfO2 thin films generated by LPD is pure and the structure is dense and continuous. The physical and chemical properties are stable, and the film thickness is around 40 nm after sufficient growth. The transmittance of HfO2 films after annealing at 500 °C is greater than 93%, the leakage current density at 1 V is 1.38× 10-6 A/cm2, and the breakdown voltage is 6.4 V. At the same time, based on the capacitance value at 1 MHz, the dielectric constant of the HfO2 film is estimated to be around 20.4.
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