A two-step processing method is developed for the fabrication of micro- and nano hierarchical wick structures on silicon substrate. Deep reaction ion etching (DRIE) was used to fabricate the primary wick, while the secondary wick structure was formed by electrochemical (EC) etching on the surface of the primary wick. The processing results show that the fabricated hierarchical wick structures consist of dense arrays of microscale trench and a uniformly distributed nanoporous layer with pore diameters less than 50nm. The merit of these hierarchical structures was demonstrated by thermal tests on the silicon vapor chamber integrated with such wicks. A prototype of the vapor chamber with 30 mm x 25 mm x 1.5 mm in dimension was developed as a passive heat spreader for thermal management of electronics. Thermal performance results indicate that the integration of hierarchical wick structures can significantly reduce the thermal resistance by similar to 50% compared with samples integrated with only microwick structures. Such an optimization on the thermal resistance indicates that integration of such hierarchical wick could be a promising method for the optimization of silicon-based thermal management devices.

Thin film boiling (TFB) is an intensive phase change heat transfer mode and therefore is highly expected to cope with those urgent heat dissipation requirements of chips and electronic devices. Theoretically, the upper limit of critical heat flux (CHF) for TFB can be 5000 W/cm2. However, the highest CHF of TFB reported in the literature is 1230 W/cm2. To fill the gap, research efforts were made on both the experimental sample and the experimental procedure. The unilateral fixation of the experimental samples was upgraded to bilateral fixation so as to improve the pressure-bearing capacity of the samples. TFB experiments under constant driving pressure difference proved that bilateral fixation indeed helped samples to withstand higher liquid pressure and consequently contributed to improved heat flux, but the measured CHF was only around 1400 W/cm². It was attributed to the inherent operating procedures of the constant driving pressure mode that when the liquid pressure was relatively high, the sample was under extreme mechanical condition at the very beginning of the experiment, therefore was fragile and would probably break before achieve the theoretical CHF for that pressure. Accordingly, two alternative liquid pressure and heating power variation approaches for manipulating TFB were proposed and applied. In the asynchronous variation approach, the liquid pressure was increased in a stepping mode, with pressure difference of several hundred Pa between two steps. For each pressure step, the heating power increased until approaching the theoretical CHF of that pressure. Therefore, it is analogous to automatic transmission (AT) with finite gear ratios. In the simultaneous variation approach, the liquid pressure and heating power were varied with smaller step and higher frequency. Consequently, the ultimate situation is the simultaneous variation of liquid pressure and heating power, which is analogous to continuously variable transmission (CVT). In these ways, the experimental samples stayed in a relatively relaxed state and the achieved CHF results were notably improved to the range of 1500 to 2000 W/cm2, and a record-breaking high CHF of 2074 W/cm2 was also obtained.

Evaporation from nanopores is of great interest in nature and many industrial applications. Therefore, understanding the transport processes within a pore requires integrating the dynamics of vapor and liquid flow, and interfacial interactions are essential. The vapor movement is classified as free molecular flow due to the modest size of the pore (about 100 nm) compared to the mean free path (roughly 1.1 mu m). Our research will begin by determining the possibility of liquid molecules evaporating from the surface and entering the pore and the probability of vapor molecules condensing back onto the surface once they reach the pore's end. We then investigate the effects of various operating factors to identify settings that optimize nanopore evaporation.

随着集成电路制程趋于极限,登纳德缩放定律逐步失效,芯片的功率密度逐渐提升,尤其是在5G、物联网以及高性能计算快速发展的驱动下,单芯片面积也在增大,热耗散问题日趋严重,传统的冷却方式已无法保证芯片的可靠工作.将热沉制备在芯片内部可以避免封装材料的导热热阻和多层界面热阻,提升冷却性能和冷却效率.学术界针对芯片的嵌入式微流体冷却开展了大量卓有成效的研究和探索,不断提出新型通道结构设计方案,包括平行长直通道、歧管通道、射流通道等.旨在于优化泵功和热阻,在小压降下实现高效冷却.然而,随着芯片面积的增大,在限域空间实现高效冷却将更加困难,工艺难度和制造成本限制了嵌入式液冷的大规模商业化使用,目前在实际IC芯片内演示的冷却方案验证了嵌入式冷却的性能,但复杂度高,兼容性差,冷却性能有待进一步提升.尤其是在3D封装架构下,需要提出兼容小型化、高密度封装的通道结构,通过协同设计,在保证电学互连的前提下实现层间冷却.在优化通道结构设计的同时,还需要简化工艺,降低成本,提升嵌入式微流体冷却的工艺可靠性和长期工作可靠性,才能推进嵌入式微流体冷却技术的实际应用.

以GaN为代表的新一代半导体材料具有宽禁带、高电子饱和速率、高击穿场强等优异的电学性能，使得射频、电力电子器件有了具备更高功率能力的可能，目前限制器件功率提升的主要瓶颈是缺少与之匹配的散热手段。具有极高热导率的金刚石已成为提升器件散热能力的重要材料，学术界针对金刚石与功率器件集成的先进热管理技术已经开展了大量有益的研究与探索，但是由于金刚石具有极强的化学惰性和超高的硬度，在实际集成和工艺加工过程中，金刚石-GaN界面容易出现热性能和可靠性问题，甚至会导致器件失效。对金刚石热管理技术的研究进展和存在的问题进行了深入分析，并对未来主要工作方向做了展望。

Since the embedded microchannel heat sink has become a potential thermal management technology developed for the next generation of power devices to ensure the reliability of the embedded microchannel chip. The finite element simulation technology was used to investigate the influence of different shapes of liquid inlets and outlets of the embedded microchannel chip during the flip-chip bonding process and carried out experiments to prove the simulation prediction. The results show that the optimized design of the shapes of liquid inlets and outlets can effectively reduce the stress performance of the chip. The maximal thermal stress of chips will decrease by more than 70 %. To the best of our knowledge, there is currently no research report in this area in the world. This work is of great significance in promoting the practical application of microfluidic chips.

The heat dissipation of power amplifier (PA) chips is one of the biggest challenges in the development of miniaturized state of art glass-based high-power RF modules. Glass has excellent electrical properties, but the extremely poor thermal conductivity of it also brings many barriers in the application. Its (quartz glass) thermal conductivity is only 1/93 of that of silicon, so there will be a problem of poor heat dissipation. In recent years, there has been an increasing amount of literature on microfluidic cooling technology and this method was demonstrate as an efficient way in cooling application. In this article, we designed, fabricated, and tested a Si-Glass microchannel heat sink, which took advantage of the high thermal conductivity of silicon to deal with the insufficient thermal conductivity of the glass interposer. Finite element simulation was used to study the thermal property of the Si-Glass heat sink and a multi-parameter optimal method was used to design the geometrical parameters, including the number of flow channels and other geometrical parameters of the heat sink. Then the aforementioned microchannel heat sinks were fabricated using cleanroom fabrication on 4-inch silicon and glass wafers. To complete the thermal test, the Thermal Demonstration Vehicles (TDVs) were fabricated by bonding the sample onto a customized PDMS holder for fluid connections with the flow loop. A programmable power source was used to heat the TDV in a stepwise manner, and a syringe pump was used to supply the liquid to cool the heat sink. Results show that the heat sink can dissipate heat flux greater than 150W/cm2with substrate temperature lower than 100°C.

The thermal management of a super high heat flux hot spot is critical for the utilization of the new generation semiconductor materials. Among these approaches, the embedded cooling technology has been demonstrated as an efficient way to cool the high heat flux devices. In this work, a silicon base microchannel heat sink was designed and fabricated to cool the hot spots from 50 um to 5000 um. Hotspots were set right above the inlet of the microchannel heat sink and the cooling performance of them were tested via a thermal test vehicle (TTV). The experimental results showed that our thermal management system could dissipate a heat flux of up to 20 kW/$cm^{2}$ in the hotspot of 50 $\mu m\times 50 \mu$ m while temperature rise of the heated area maintained below 270°C.

Ultrahigh heat flux of over 1 kW/cm2 can be achieved by a new thin film boiling regime, of which the variation of boiling curve is considerably different from that of pool boiling. However, there is a lack of quantitative analysis for the distinctive thin film boiling. In this work, comprehensive comparison was made between the well-studied pool boiling and the newly-achieved thin film boiling. The boiling curve of thin film boiling was divided into three segments and mathematical models were set up for each segment in a way that correlations for pool boiling were adopted and modified according to the similarity and difference between pool boiling and thin film boiling, respectively. It was found that the modeling results agreed very well with the experimental results, indicating that the hybrid model revealed the underlying mechanism for the unique behavior and ultrahigh heat flux of the thin film boiling. In brief, the higher heat transfer coefficient or larger slope of the boiling curve was related to the special water supply mode of thin film boiling, in which the water flowed vertically through the heat surface and consequently enhanced heat transfer by promoting the spread of superheated layer and the bubbles on the heating surface. As for the ultrahigh heat flux and the unique negative slope of the boiling curve, it was attributed to the very thin yet continuously decreased thickness of the liquid layer, which was another essential feature of the thin film boiling. The hybrid model in this work can provide both quantitative insight for fundamental understanding and future guidance for practical application of thin film boiling.

Engineering surfaces with excellent wicking properties is of critical importance to a wide range of applications. Here, we report a facile method to create superhydrophilic nanoporous micropillared surfaces of silicon and their applicability to superwicking. Nanopores with a good control of the pore depth are realized over the entire surface of three-dimensional micropillar structures by electrochemical etching in hydrofluoric acid. After rinsing in hydrogen peroxide, the nanoporous micropillared surface shows superhydrophilicity with the superwicking effect. The entire spreading process of a water droplet on the superhydrophilic nanoporous micropillared surface is completed in less than 50 ms, with an average velocity of 91.2 mm/s, which is significantly faster than the other wicking surfaces reported. Owing to the presence of nanopores on the micropillar array, the wicking dynamics is distinct from the surfaces decorated only by micropillar arrays. The spreading dynamics of a water droplet shows two distinct processes simultaneously, including the capillary penetration between micropillars and the capillary imbibition into the nanopore's interior. The wicking dynamics can be described by the two stages separated by the time when the contact line starts to recede. The transition between the two wicking regimes is due to the increasing effect of the imbibition of the bulk droplet by the nanopores. While a similar transition of the wicking dynamics is shown on the surfaces with different pore depths, the nanopore structure with a greater depth causes a greater amount of imbibition to slow down the spreading and promote superwicking.

A large variety of synthetic methods have been developed for hierarchically porous materials by which the performance of a wide range of applications can be dramatically enhanced. Herein, hierarchically porous micropillar arrays are demonstrated by employing electrochemical etching to silicon micropillars. The approach relies on the steering of current flow through the three-dimensional silicon-electrolyte interface to enable nanopores to grow on the entire surface of the micropillars, simultaneously. The pores grow perpendicular to the surface of the micropillars, whereas the pore diameter and porosity vary depending on the locations of the surfaces. The finite element analysis shows that the spatial variation of the pore diameter and porosity is determined by the distribution of current density. Further, the thickness of the porous layer can be tuned by etching time so that sponge-like porous structures are conveniently obtained by regulating the etching time. In addition to the effect of current density flowing through the etched surfaces, the growth of pores also depends on the crystal orientations of the etched surfaces. The etching results on square micropillar arrays and microgroove arrays show that the growth direction and rate of nanopores inside the microstructure also depend on the exposed crystal planes. The facile characteristics of the fabrication method can serve as an effective route for a wide range of applications of porous materials with enhanced capabilities.

Recent research has shown that bacteria can complete information exchange with other groups via physical or chemical properties of signal molecules which is known as quorum sensing (QS), The communication of microorganism groups has a valuable function in regulating the physiological behavior of bacteria. In order to explore the cell to cell communication, we fabricated a gelatinous substrate with micrometer scale inverted pyramid array structure, which can coniine a large population of bacteria for localized fluorescence detection of Escherichia Coli (E. Coli) under variable growing conditions. The fabricated substrate enables different kinds of bacteria's segregation physically and communication chemically. A two-step embossing process was developed to replicate the inverted pyramid patterns from a silicon master to the gelatin substrate. The cell to cell communication was verified by the fluorescence detection of the E. Coli. According to the specific changes in quantity and the fluorescence intensity of E. Coli, we have demonstrated that Pseudomonas aeruginosa with different phenotypes suspended out of the matrix present different effects to the growth of E. Coli within the micrometer scale inverted pyramid.

In this paper, we report a simple fabrication process of whole Teflon superhydrophobic surfaces, featuring high-aspect-ratio (>20) nanowire structures, using a hot embossing process. An anodic aluminum oxide (AAO) membrane is used as the embossing mold for the fabrication of high-aspect-ratio nanowires directly on a Teflon substrate. First, high-aspect-ratio nanowire structures of Teflon are formed by pressing a fluorinated ethylene propylene (FEP) sheet onto a heated AAO membrane at 340 °C, which is above the melting point of FEP. Experimental results show that the heating time and aspect ratios of nanopores in the AAO mold are critical to the fidelity of the hot embossed nanowire structures. It has also been found that during the de-molding step, a large adhesive force between the AAO mold and the molded FEP greatly prolongs the length of nanowires. Contact angle measurements indicate that Teflon nanowires make the surface superhydrophobic. The reliability and robustness of superhydrophobicity is verified by a long-term (~6.5 h) underwater turbulent channel flow test. After the first step of hot-embossing the Teflon nanowires, microstructures are further superimposed by repeating the hot embossing process, but this time with microstructured silicon substrates as micromolds and at a temperature lower than the melting temperature of the FEP. The results indicate that the hot embossing process is also an effective way to fabricate hierarchical micro/nanostructures of whole Teflon, which can be useful for applications of Teflon material, such as superhydrophobic surfaces.

In this paper, a three-dimensional (3D) tandem Si/ITO/WO3 photoelectrode system with a high-aspect-ratio (HAR) micropost array structure based on a 'Z-scheme' is designed to enhance photocatalytic performance. To produce such a photoelectrode system, microposts were first fabricated on a Si substrate by deep reactive ion etching (DRIE), followed by deposition of an indium tin oxide (ITO) layer and tungsten trioxide (WO3) layer on microposts. The photocatalytic performance was verified by the degradation of methylene blue (MB, C16H18ClN3S) under visible light conditions. In the photocatalytic test, photoelectrode samples of a 0.5 cm2 footprint were used to degrade 15 ml MB (10 mg l−1). Experimental results indicate that the 3D micropost WO3/ITO/Si structure has a higher efficiency compared with the 2D planar WO3/ITO/Si structure. A decrease of 83.6% in MB concentration within 30 min is observed in the preliminary degradation test. The HAR photoelectrode configuration can dramatically increase the surface-to-volume ratio, not only increasing the total incident light absorption efficiency, but also facilitating the oxidation–reduction reaction in the semiconductor-liquid interface.

Inspired by the Salvinia effect, we report the fabrication and characterization of a novel "sticky" superhydrophobic surface sustaining a Cassie-Baxter wetting state for water droplets with high contact angles but strong solid-liquid retention. Unlike superhydrophobic surfaces mimicking the lotus or petal effect, whose hydrophobicity and droplet retention are typically regulated by hierarchical micro- and nanostructures made of a homogeneous material with the same surface energy, our superhydrophobic surface merely requires singular microstructures covered with a hydrophobic coating but creatively coupled with hydrophilic tips with different surface energy. Hydrophilic tips are selectively formed by meniscus-confined electrodeposition of a metal (e.g., nickel) layer on top of hydrophobic microstructures. During the electrodeposition process, the superhydrophobic surface retains its plastron so that the electrolyte cannot penetrate into the cavity of hydrophobic microstructures, consequently making the electrochemical reaction between solid and electrolyte occur only on the tip. In contrast to typical superhydrophobic surfaces where droplets are highly mobile, the "sticky" superhydrophobic surface allows a water droplet to have strong local pinning and solid-liquid retention on the hydrophilic tips, which is of great significance in many droplet behaviors such as evaporation.

In this paper, a three-dimensional (3D) tandem Si/ITO/WO3 photoelectrode system with a high-aspect-ratio (HAR) micropost array structure based on a 'Z-scheme' is designed to enhance photocatalytic performance. To produce such a photoelectrode system, microposts were first fabricated on a Si substrate by deep reactive ion etching (DRIE), followed by deposition of an indium tin oxide (ITO) layer and tungsten trioxide (WO3) layer on microposts. The photocatalytic performance was verified by the degradation of methylene blue (MB, C16H18ClN3S) under visible light conditions. In the photocatalytic test, photoelectrode samples of a 0.5 cm(2) footprint were used to degrade 15 ml MB (10 mg l(-1)). Experimental results indicate that the 3D micropost WO3/ITO/Si structure has a higher efficiency compared with the 2D planar WO3/ITO/Si structure. A decrease of 83.6% in MB concentration within 30 min is observed in the preliminary degradation test. The HAR photoelectrode configuration can dramatically increase the surface-to-volume ratio, not only increasing the total incident light absorption efficiency, but also facilitating the oxidation-reduction reaction in the semiconductor-liquid interface.

This paper reports an enhanced photocatalysis system for organic pollutants degradation, using high-aspect-ratio (HAR) Si/ITO/WO 3 micropost photoelectrodes, fabricated by deep reactive ion etching (DRIE) and sputtering. Compared with traditional Titanium Dioxide (TiO 2 ) photoelectrodes, Tungsten trioxide (WO 3 ) coupled with Si can absorb visible light. Besides, an optimized HAR electrode configuration can dramatically increase the surface-to-volume ratio, not only increasing the total incident light intensity, but also facilitating the oxidation-reduction reaction in the semiconductor-liquid interface. The preliminary Methylene Blue (MB) (C 16 H 18 C1N 3 S) degradation test showed that about 83.4% of MB can be degraded within 30 min.

Microinjection is a promising tool for microdroplet generation, while the microinjection for microdroplets generation still remains a challenging issue due to the Laplace pressure at the micropipette opening. Here, we apply a simple and robust substrate-contacting microinjection method to microdroplet generation, presenting a size-adjustable microdroplets generation method based on a critical injection (CI) model. Firstly, the micropipette is adjusted to a preset injection pressure. Secondly, the micropipette is moved down to contact the substrate, then, the Laplace pressure in the droplet is no longer relevant and the liquid flows out in time. The liquid constantly flows out until the micropipette is lifted, ending the substrate-contacting situation, which results in the recovery of the Laplace pressure at the micropipette opening, and the liquid injection is terminated. We carry out five groups of experiments whereupon 1600 images are captured within each group and the microdroplet radius of each image is detected. Then we determine the relationship among microdroplet radius, radius at the micropipette opening, time, and pressure, and, two more experiments are conducted to verify the relationship. To verify the effectiveness of the substrate-contacting method and the relationship, we conducted two experiments with six desired microdroplet radii are set in each experiment, by adjusting the injection time with a given pressure, and adjusting the injection pressure with a given time. Then, six arrays of microdroplets are obtained in each experiment. The results of the experiments show that the standard errors of the microdroplet radii are less than 2% and the experimental errors fall in the range of ±5%. The average operating speed is 20 microdroplets/min and the minimum radius of the microdroplets is 25 μm. This method has a simple experimental setup that enables easy manipulation and lower cost.