Dendritic material as a dry-release sacrificial layer

A dry-release process using highly structured dendritic material, specifically, hyperbranched polymers (HBP's), has been developed. A particular HBP under study, known as HB560, has been characterized and successfully integrated with microelectromechanical systems processing. An array of electroplated nickel cantilever beams 100 μm×100 μm ~1000 μm in length has been successfully fabricated and dry released. The required release time is 10 min at 600°C in O₂ . Single open-ended microchannels were fabricated to determine the etch time and tunneling length achieved using HB560 as a sacrificial material. The time improvement for the sacrificial release is on the order of 40× compared to standard HF wet-etch processes. Etch lengths of 1 cm have been successfully demonstrated with a sacrificial layer aspect ratio of 1600. A photosensitive version of the dendritic material has also been synthesized and characterized to reduce the process steps     

Releasing high aspect ratio SU-8 microstructures using AZ photoresist as a sacrificial layer on metallized Si substrates

This paper presents a successful method for releasing high aspect ratio SU-8 micro-structures by the use of positive photoresist (AZ 4620) as sacrificial layer. The AZ 4620 photoresist sacrificial layer was dissolved by the SU-8 developer (propylene glycol monomethyl ether acetate). Thus, this process reduces the need for complex microfabrication steps and equipments which are otherwise required in traditional methods using metal sacrificial layers. The current method is both cost-effective and time-effective because no additional releasing method or material is needed to remove the fabricated SU-8 structures. Further, the influence of surface energy on the adhesion between Si and SU-8 was demonstrated and metallic thin layer coating on Si was employed to further reduce the lift-off duration. The results obtained showed that the duration for lift-off of SU-8 structures from metal (Al) coated Si substrate is much lower (approximately 90 % time saving) and the surface morphology of the released structures has lesser micropore concentration compared to the process employing bare Si as the substrate. In both processes AZ 4620 was the sacrificial layer whereas the metalized Si substrate could be re-used.     

RF MEMS开关在牺牲层工艺上的改进

通过对传统的RF MEMS开关采取在信号线上电镀桥墩、改进桥梁的形状以及在桥背面设计接触点的新颖方法,使得RF MEMS开关的下拉电压减小、开关时间缩短和可靠性提高.在工艺上,特别采用了对聚酰亚胺牺牲层进行全刻蚀和半刻蚀的改进加工流程来实现桥背面的接触点.测试结果表明:开关的下拉电压为28V,最低开关时间为0.8μs,开关寿命达7×105次,0～10GHz的插入损耗在0～0.5dB,隔离度为35～45dB.     

牺牲层腐蚀改进模型与模拟研究

牺牲层腐蚀主要受腐蚀液的扩散过程制约,由扩散方程决定.扩散系数在腐蚀过程中随温度和腐蚀液浓度变化而改变.文中对改进的腐蚀模型给出有限差分算法,由每一时刻溶液在具体位置的浓度值得出扩散系数,再由Topography模型计算前端面的腐蚀情况得到腐蚀前端行进的轮廓线.并编程对一些MEMS结构的释放过程进行仿真,最后给出实验验证.     

Preparation of sacrificial layer for MEMS devices by lift-off technology

To simplify the preparation of sacrificial layer in micro-electromechanical system structure, new processes have been developed. By using lift-off technology, sacrificial layer was selectively deposited into the pit that prepared for sacrificial layer releasing. Then a short time polishing process was used to remove the burrs around the pit. This method offers several advantages including reducing the difficulty of polishing and hence processing cost. Methods and apparatuses to provide a continuously smoothly sacrificial layer surface in the pit were disclosed. However, it is important to control the homogeneity of filling and avoid the shadow effect at the corner of the pit. The unpadded regions would form a steep step and cause the cracking of structure layer. This problem was discussed and solved by rotating the tilted wafer during sacrificial material deposition. The surface roughness after the preparation process of sacrificial layer was measured. The root mean square roughness of sacrificial layer was 1.247 nm and reduced to 0.861 nm after a short time polishing process. Finally, a film bulk acoustic wave resonator with stacked Mo/AlN/Mo films had been fabricated on the sacrificial layer based on this method.     

In situ fabrication of SU-8 movable parts by using PAG-diluted SU-8 as the sacrificial layer

In this paper we proposed a novel technology to make SU-8 movable parts in situ by using PAG-diluted SU-8 or SU-8R, a SU-8 solution with no photoacid generator (PAG) content, as the sacrificial layer. Since they are not or less sensitive to UV light the unexposed bottom layer in UV lithography will be dissolved to release the movable components during the final develop in PGMEA (Propylene Glycol Monomethyl Ether Acetate). The use of PAG-diluted SU-8 or SU-8R as a sacrificial layer offers several advantages including significant reduction in processing steps. It becomes the simplest technique currently available for in situ fabrication of SU-8 movable parts. In this paper the lithographic sensitivities of SU-8 as a function of the PAG concentration, detailed fabrication process and examples of fabricated SU-8 movable parts will be presented.     

A new sacrificial layer method of LIGA technology to fabricate movable part of a gripper

 Movable microstructures are required for many applications in accelerator sensors, microvalves, micromotors, grippers and so on. With the LIGA technique, movable components can be fabricated directly by using sacrificial layer technology. This is considerably extended by the application of the LIGA technique. Normally thin metallic layers are sputtered onto an insulating substrate (e.g. silicon wafer or ceramic) and patterned by conventional photolithography and wet etching. They are used as a metalized layer and a sacrificial layer. The movable parts of the microstructures are positioned on the surface of the sacrificial layer, whereas the fixed parts are placed on the metalized area of the substrate. After stripping the resist and the sacrificial layer, the movable parts on the sacrificial layer are finished and the fixed parts remain firmly on the metalized layer. This process is rather complicated. A new technology to produce the movable parts is developed in our Lab. Firstly the normal LIGA process is used to make the sample with both metal and resist structures. The sacrificial layer pattern will be placed on the sample surface with UV lithography. A metal layer is sputtered on the sample and sacrificial layer surface as a metalized layer. By electroplating, the metalized layer will grow up to the milimeter thickness and be used as the fixed substrate. Finally removing the nonmetal substrate, resist and the sacrificial layer, the movable parts could be completed. As an example, a magnetic gripper structure is designed and fabricated by this method.     

Slotted capacitive microphone with sputtered aluminum diaphragm and photoresist sacrificial layer

In this paper, we have fabricated a new microphone using aluminum (Al) slotted perforated diaphragm and back plate electrode, and photoresist (AZ1500) sacrificial layer on silicon wafer. The novelty of this method relies on aluminum diaphragm includes some slots to reduce the effect of residual stress and stiffness of diaphragm for increasing the microphone sensitivity. The acoustic holes are made on diaphragm to reduce the air damping, and avoid the disadvantages of non standard silicon processing for making back chamber and holes in back plate, which are more complex and expensive. Photoresist sacrificial layer is easy to deposition by spin coater and also easy to release by acetone. Moreover, acetone has a high selectivity to resist compared to silicon oxide and Al, thus it completely removes sacrificial resist without incurring significant damage silicon oxide and Al. The measured zero bias capacitance is 17.5 pF, and its pull-in voltage is 25 V. The microphone has been tested with external amplifier and speaker, the external amplifier was able to detect the sound waves from microphone on speaker and oscilloscope. The maximum amplitude of output speech signal of amplifier is 45 mV, and the maximum output of MEMS microphone is 1.125 μV.     

Adhesion of Ni-structures on Al2O3 ceramic substrates used for the sacrificial layer technique

 This study presents an investigation of the adhesion properties of a chromium-gold-titanium layer system, which is used in the LIGA process to create moveable microstructures. The main purpose has been the improvement of the process parameters to increase yield reliability. Three mechanisms affecting the adhesion have been identified. As a consequence of humidity adsorbed H₂O reacts with Al₂O₃ to AlO(OH) (aluminum meta hydrates), which does not bond to the sputtered chromium layer. Thus the hydrate must be removed by cleaning the surface with Ar⁺-ions. Tight layers without pores could be realized by optimization pressure and temperature during sputtering of chromium and gold. Thus, diffusion of chromium or penetration of etchants into the gold layer as well as impact or diffusion of titanium into the gold layer could be prevented. In addition, a copper layer was introduced as a further intermediate layer by electroforming to improve the formation of stable nickel alloys at the interface between the sputtered gold and the electroplated nickel. These measures resulted in an improvement of the adhesion, so that full functional acceleration sensors were produced with a high yield.     

A new process to fabricate the electromagnetic stepping micromotor using LIGA process and surface sacrificial layer technology

 In this paper, a new process to fabricate an electromagnetic stepping micromotor using surface sacrificial layer technology (SSLT) is illustrated, and the SEM photo of the stepping micromotor is showed. The torque of the stepping micromotor with maximum torque of 60 μNm is directly calculated by using electromagnetics laws and the law of conservation of energy. The stator and the shaft and the rotor of the micromotor with the material of nickel are first all fabricated by normal LIGA process at the same time. The sacrificial layer structure with the material of AZ resist is made on the surface of the rotor by using SSLT. The stator and the shaft are fixed together with copper substrate instead of the old Ti substrate by electroplating. After removing the Ti substrate, PMMA resist and the sacrificial layer structure, the rotor is separated from the stator and new copper substrate, and can rotate on the new substrate driven by magnetic force. The four coils with 300 turns each are wound on iron bars by hand using microscope and stepping motor. The bars are assembled by hand into the stator holes from rear of new copper substrate to form a magnetic circuit with the stator and the rotor. A power supply with four consecutive pulses provides the current for the coils wound on the iron bars and produces the magnetic force to drive the rotor to run with the speed of 60 rpm.     

Kernels as features: On kernels, margins, and low-dimensional mappings

Kernel functions are typically viewed as providing an implicit mapping of points into a high-dimensional space, with the ability to gain much of the power of that space without incurring a high cost if the result is linearly-separable by a large margin γ. However, the Johnson-Lindenstrauss lemma suggests that in the presence of a large margin, a kernel function can also be viewed as a mapping to a low-dimensional space, one of dimension only $\tilde{O}(1/\gamma^2)Kernel functions are typically viewed as providing an implicit mapping of points into a high-dimensional space, with the ability to gain much of the power of that space without incurring a high cost if the result is linearly-separable by a large margin γ. However, the Johnson-Lindenstrauss lemma suggests that in the presence of a large margin, a kernel function can also be viewed as a mapping to a low-dimensional space, one of dimension only . In this paper, we explore the question of whether one can efficiently produce such low-dimensional mappings, using only black-box access to a kernel function. That is, given just a program that computes K(x,y) on inputs x,y of our choosing, can we efficiently construct an explicit (small) set of features that effectively capture the power of the implicit high-dimensional space? We answer this question in the affirmative if our method is also allowed black-box access to the underlying data distribution (i.e., unlabeled examples). We also give a lower bound, showing that if we do not have access to the distribution, then this is not possible for an arbitrary black-box kernel function; we leave as an open problem, however, whether this can be done for standard kernel functions such as the polynomial kernel. Our positive result can be viewed as saying that designing a good kernel function is much like designing a good feature space. Given a kernel, by running it in a black-box manner on random unlabeled examples, we can efficiently generate an explicit set of features, such that if the data was linearly separable with margin γ under the kernel, then it is approximately separable in this new feature space. Editor: Philip Long A preliminary version of this paper appeared in Proceedings of the 15th International Conference on Algorithmic Learning Theory. Springer LNAI 3244, pp. 194–205, 2004.     

步态驱动的四足动物低维物理运动生成方法

目的 为了解决四足动物运动数据难以获取的问题,建立一种快速易用的四足动物运动重建和制作途径,提出了一种面向四足动物的实时低维运动生成方法。方法 首先,建立以质点、刚体和弹簧为基础的低维物理解算器,将四足动物骨架抽象为低维物理模型;其次,依据步态模式建立足迹约束,自脚向上分肢体求解全身物理质点的运动信息;最后,依据通用约束修正后的质点位置,反算全身动画骨骼节点,生成目标运动。结果 针对不同步态、不同体型、不同风格的四足动物进行多组实验,本文方法能够达到330帧/s的生成速度,且具备良好的视觉效果和通用性。结论 本文方法的输入数据易于学习和获取,计算过程实时稳定,可以快速生成符合视觉真实感的多风格运动数据。     

Facial-expression recognition based on a low-dimensional temporal feature space

Multimedia Tools and Applications - This paper suggests a facial-expression recognition in accordance with face video sequences based on a newly low-dimensional feature space proposed. Indeed, we...     

Polysilicon sacrificial layer etching using ClF3 for thin film encapsulation of silicon acceleration sensors with high aspect ratio

We present a new thin film encapsulation technique for surface micromachined sensors using a polysilicon multilayer process. The main feature of the encapsulation process is that both the sacrificial layer above the silicon sensor structure and the cap layer consist of epitaxial polysilicon. The sacrificial layer is removed by chlorine trifluoride (ClF₃) plasmaless gas-phase etching through vents within the cap layer. The perforated cap membrane is sealed by a nonconformal oxide deposition. The method has been applied to a silicon surface micromachined acceleration sensor with high aspect ratio structures, but is broadly applicable. Capacitance–voltage measurements have been performed to show the electrical functionality of the accelerometer.     

MgO sacrificial layer for micromachining uncooled Y-Ba-Cu-O IRmicrobolometers on Si3N4 bridges

This paper describes a new micromachining technique for fabrication of semiconducting yttrium barium copper oxide (YBCO) microbolometers using magnesium oxide (MgO) as the sacrificial layer. This type of bolometer can be operated at room temperature, providing a low-cost alternative for more expensive cryogenically cooled thermal detectors used for infrared (IR) imaging. The new micromachining techniques described here would enable the fabrication of YBCO IR focal plane array (FPA) with CMOS signal processing circuitry. Devices were fabricated by growing YBCO films on 4000-Å-thick suspended Si₃N₄ membranes measuring 40×40 μm² in area and extended over micromachined air gaps, which provide the low thermal conductivity that is required for high responsivity. The gap was created by etching an MgO sacrificial layer. This is the first example of using MgO in this type of application. The MgO sacrificial layer technique is fully CMOS compatible and presents no major fabrication challenges. Thermal conductivities achieved in vacuum with the Si₃N₄ suspended structures were on the order of 10^-7 W/K, yielding an effective thermal isolation for bolometer operation. Optical characterization has shown responsivity up to 60 kV/W and detectivity over 10⁸ cm.Hz^1/2/W to black-body IR radiation, indicating that this technology is a suitable candidate for low-cost thermal imaging     

Fabrication and characterization of Pb-free transparent dielectric layer for plasma display panel

Glasses within the Bi₂O₃–B₂O₃–BaO–ZnO system were examined as potential replacements for PbO-based glass frits with low firing temperatures. These frits are used in the transparent dielectric layer of plasma display panels (PDP). The glass transition temperature (T_g) of the prepared glasses varied between 450 and 460 °C. These glasses display dynamic dielectric properties, high transparency and thermal expansion as well as matching well with substrate glass. The thermal coefficient of expansion (TCE) was with the desired range of 81–86×10⁻⁷/K. Moreover, when the screen printed film was heat-treated at 570 °C for 30 min, optical transmittance (83%), root-mean square (rms) roughness (177.6 Å), dielectric constant (10.25) and withstand voltage (4.15 kV) satisfied the requirements necessary for transparent dielectric layers to be used in PDP applications.     

Manufacture of a micro-sized piezoelectric ceramic structure using a sacrificial polymer mold insert

There have been technical limitations to manufacture microstructures due to difficulty of demolding during replication process of high aspect ratio microstructure in mass production technologies. In the present study, the fabrication of a novel sacrificial micro mold insert and powder injection molding process using such a micro mold insert is proposed and developed. It utilizes a synchrotron radiation to fabricate the shape of polymer based sacrificial mold inserts and then these mold inserts were exposed at X-ray once more to adjust its solubility. This second X-ray exposure facilitates dissolving of mold inserts instead of demolding process which have difficulties like pattern collapses or defects in case of precise replication process. In this manner, severe problems of demolding process in conventional mass production technologies can be efficiently overcome. To verify the usefulness of the proposed technique, polymer based micro mold inserts with several tens of micrometer sized structure for piezoelectric sensor applications were fabricated using X-ray micromachining process radiated synchrotron. The solubility of mold inserts were optimized by the second X-ray exposure without an X-ray mask and then subsequent powder injection molding process was utilized with a piezoelectric based material. Finally, piezoelectric ceramics with micrometer-scale and high aspect ratio of 5 were successfully fabricated, verifying that the present sacrificial mold system is useful for the precise replication process such as the fabrication of microstructure with high aspect ratio or complicated structure.     

Microfabricated self-resonant structure as a passive wireless dielectric constant and conductivity sensor

This paper describes a low cost, passive wireless dielectric constant and conductivity sensor using a microfabricated inductor with interdigitated capacitors (IDC). A self-resonant-structure (SRS) is designed by incorporating IDC electrodes in the inter-winding space of the inductor. The distributed capacitance and conductance of the sensor is affected by dielectric constant (ε) and conductivity (σ) of its environment or material under test (MUT). The ε and σ can be used to provide information about the surrounding environment. This serves as an impedance transducer changing the resonant frequency and phase dip of the SRS. The SRS is interrogated using a non-contact inductively coupled reader coil. The change in resonance frequency and phase dip of the SRS is used to detect material properties of the environment/MUT. The relationship between sensor layout and coupling factor between sensor and reader is investigated. Optimizations of the coupling factor based on this relationship are discussed. IDC design trade-offs between the sensor’s sensitivity and coupling factor are also investigated. The sensor’s response to variety of liquid MUTs with a wide range of dielectric constant and conductivity is presented.     

Low voltage organic devices and circuits with aluminum oxide thin film dielectric layer

Low voltage operating organic devices and circuits have been realized using atomic layer deposition deposited aluminum oxide thin film as dielectric layer. The dielectric film has per unit area capacitance of 165 nF/cm2 and leakage current of 1 nA/cm2 at 1 MV/cm. The devices and circuits use the small-molecule hydrocarbon pentacene as the active semiconductor material. Transistors,inverters,and ring oscillators with operating voltage lower than 5 V were obtained. The mobility of organic field-effect transis...