Ho-Chiao Chuang

The development of an atom chip with through silicon vias for an ultra-high-vacuum cell

This paper describes the development, fabrication and examination of an atom chip through silicon vias (TSV), which is anodically bonded with a Pyrex glass cell to form an ultra-high-vacuum system for the application of Bose–Einstein condensation (BEC) experiments. The silicon via is etched by the inductively coupled plasma reactive ion etch and filled by copper plating technology. The metal wires on both sides of the atom chips are patterned by the lithography process. Three different sizes of TSV are made and tested by continuously applying a maximum current of 17 A under the vacuum (70 Torr) and in air. In addition, after the thermal cycling of an anodic bonding process (requested at 350 °C) and a high electric field of 1000 V m−1, the TSV on atom chips can still hold the ultra-high vacuum (UHV). The conductive and vacuum yields of the TSV improved from 50% to 100% and from 75% to 81.25%, respectively after the modification of the fabrication process. Finally, the UHV test of TSV on atom chips at room temperature can be reached at 8 × 10−10 Torr, thus satisfying the requirements of atomic physics experiments under the UHV environment.

The fabrication of through-wafer interconnects in silicon substrates for ultra-high-vacuum atom-optics cells

This paper describes a new method for fabricating through-wafer interconnects in atom trapping chips used in ultra-high-vacuum atom-optics cells for Bose?Einstein condensation (BEC) experiments. A fabrication process was developed which uses copper electroplating to seal the vias. The advantages of using feedthrough atom trapping chips are the simple microfabrication process and the reduction of the overall chip area bonded to the glass atom trapping cell. The results demonstrate that 11 A current can be conducted through the vias while the vacuum can be held under 4 ? 10?11 Torr at room temperature. The yield rate of fabricated via interconnects in this process after anodic bonding (requires heating to 425 ?C) is 97%.

An investigation of supercritical-CO2 copper electroplating parameters for application in TSV chips

This study uses supercritical electroplating for the filling of through silicon vias (TSVs) in chips. The present study utilizes the inductively coupled plasma reactive ion etching (ICP RIE) process technique to etch the TSVs and discusses different supercritical-CO2 electroplating parameters, such as the supercritical pressure, the electroplating current density’s effect on the TSV Cu pillar filling time, the I–V curve, the electrical resistance and the hermeticity. In addition, the results for all the tests mentioned above have been compared to results from traditional electroplating techniques. For the testing, we will first discuss the hermeticity of the TSV Cu pillars, using a helium leaking test apparatus to assess the vacuum sealing of the fabricated TSV Cu pillars. In addition, this study also conducts tests for the electrical properties, which include the measurement of the electrical resistance of the TSV at both ends in the horizontal direction, followed by the passing of a high current (10 A, due to probe limitations) to check if the TSV can withstand it without burnout. Finally, the TSV is cut in half in cross-section to observe the filling of Cu pillars by the supercritical electroplating and check for voids. The important characteristic of this study is the use of the supercritical electroplating process without the addition of any surfactants to aid the filling of the TSVs, but by taking advantage of the high permeability and low surface tension of supercritical fluids to achieve our goal. The results of this investigation point to a supercritical pressure of 2000 psi and a current density of 3 A dm−2 giving off the best electroplating filling and hermeticity, while also being able to withstand a high current of 10 A, with a relatively short electroplating time of 3 h (when compared to our own traditional dc electroplating).

A compensating system of respiratory motion for tumor tracking: design and verification.

Using the reverse motion of the treatment couch, this study offset the organ displacement generated by respiratory motion to solve the current clinical problem of increasing field sizes and safety margin expansions. This study used the self-designed simulated respiratory system (SRS) coupled with radiochromic EBT film to verify the self-developed respiratory compensation system. Pressure signals were generated from SRS to simulate abdomen movements during respiratory motion. The respiratory compensation system takes the phase of the pressure signals as the respiratory motion phase and adjusts the pressure signal gain to make the compensation signal amplitude close to the displacement of the target region. A linear accelerator is used to irradiate a 300 cGy dose on the EBT film. The experimental results suggested that the average dose percentage in the target region for the sine-wave amplitudes of 5, 10 and 15 mm with compensation improved by 6.9 ∼ 20.3% over the cases without compensation. The 80% isodose area with compensation improved by 22.8 ∼ 77.2% over the cases without compensation. The average dose percentage in the target region with compensation for respiratory motion distances of 5, 10 and 15 mm improved by 10.3 ∼ 18.7%. The 80% isodose area improved by 22.4 ∼ 55.1% after compensation. The average dose percentage of the compensated target region indicates that the proposed respiratory compensation system could improve the issue of the inability to constantly irradiate the target region caused by respiratory motion.

An autotuning respiration compensation system based on ultrasound image tracking

The purpose of this study was to develop an ultrasound image tracking algorithm (UITA) for extracting the exact displacement of internal organs caused by respiratory motion. The program can track organ displacements in real time, and analyze the displacement signals associated with organ displacements via a respiration compensating system (RCS). The ultrasound imaging system is noninvasive and has a high spatial resolution and a high frame rate (around 32 frames/s), which reduces the radiation doses that patients receive during computed tomography and X-ray observations. This allows for the continuous noninvasive observation and compensation of organ displacements simultaneously during a radiation therapy session.This study designed a UITA for tracking the motion of a specific target, such as the human diaphragm. Simulated diaphragm motion driven by a respiration simulation system was observed with an ultrasound imaging system, and then the induced diaphragm displacements were calculated by our proposed UITA. These signals were used to adjust the gain of the RCS so that the amplitudes of the compensation signals were close to the target movements. The inclination angle of the ultrasound probe with respect to the surface of the abdomen affects the results of ultrasound image displacement tracking. Therefore, the displacement of the phantom was verified by a LINAC with different inclination-angle settings of the ultrasound probe. The experimental results indicate that the best inclination angle of the ultrasound probe is 40 degrees, since this results in the target displacement of the ultrasound images being close to the actual target motion. The displacement signals of the tracking phantom and the opposing displacement signals created by the RCS were compared to assess the positioning accuracy of our proposed ultrasound image tracking technique combined with the RCS.When the ultrasound probe was inclined by 40 degrees in simulated respiration experiments using sine waves, the correlation between the target displacement on the ultrasound images and the actual target displacement was around 97%, and all of the compensation rates exceeded 94% after activating the RCS. Furthermore, the diaphragm movements on the ultrasound images of three patients could be captured by our image tracking technique. The test results show that our algorithm could achieve precise point locking and tracking functions on the diaphragm. This study has demonstrated the feasibility of the proposed ultrasound image tracking technique combined with the RCS for compensating for organ displacements caused by respiratory motion.This study has shown that the proposed ultrasound image tracking technique combined with the RCS can provide real-time compensation of respiratory motion during radiation therapy, without increasing the overall treatment time. In addition, the system has modest space requirements and is easy to operate.

The fabrication of a double-layer atom chip with through silicon vias for an ultra-high-vacuum cell

This study presents a double-layer atom chip that provides users with increased diversity in the design of the wire patterns and flexibility in the design of the magnetic field. It is more convenient for use in atomic physics experiments. A negative photoresist, SU-8, was used as the insulating layer between the upper and bottom copper wires. The electrical measurement results show that the upper and bottom wires with a width of 100 µm can sustain a 6 A current without burnout. Another focus of this study is the double-layer atom chips integrated with the through silicon via (TSV) technique, and anodically bonded to a Pyrex glass cell, which makes it a desired vacuum chamber for atomic physics experiments. Thus, the bonded glass cell not only significantly reduces the overall size of the ultra-high-vacuum (UHV) chamber but also conducts the high current from the backside to the front side of the atom chip via the TSV under UHV (9.5 × 10−10 Torr). The TSVs with a diameter of 70 µm were etched through by the inductively coupled plasma ion etching and filled by the bottom-up copper electroplating method. During the anodic bonding process, the electroplated copper wires and TSVs on atom chips also need to pass the examination of the required bonding temperature of 250 °C, under an applied voltage of 1000 V. Finally, the UHV test of the double-layer atom chips with TSVs at room temperature can be reached at 9.5 × 10−10 Torr, thus satisfying the requirements of atomic physics experiments under an UHV environment.

The Development of a Blood Leakage Monitoring System for the Applications in Hemodialysis Therapy

The purpose of this paper is to design, fabricate, and characterize of a bracelet monitoring device for blood leakage detection during the hemodialysis treatment. The design includes a photointerrupter, a Bluetooth 4 wireless module, power, and alert components. The validation results show that it only needs a very small amount of blood (0.01 ml), and takes 1.6 s to detect a blood leakage. Furthermore, the lifetime of the battery on this device is longer than the currently available commercial products. It can continuously give out an alert for 18-h long and continuously monitor up to 41 h. In addition, the transmission range of Bluetooth wireless signal can be extended to 23 m. As long as the patients wear this bracelet blood leakage detector during the hemodialysis therapy and affix the absorbent material onto the junction of fistula, any blood leakage can be detected. As the absorbent material is placed at the light sensing position of the photointerrupter, which causes the received light intensity to change during blood leakage. Once a blood leakage occurs, the absorbent material absorbs the blood due to the capillary action and triggers the alarm system. A warning light will also be activated, and a leakage occurrence is transmitted to the healthcare stations alarming healthcare workers via the Bluetooth wireless. The healthcare workers can take appropriate action immediately to prevent any risks to the patients during hemodialysis therapy. The proposed blood leakage monitoring system can improve the current medical approach for the hemodialysis therapy.

Design, microfabrication and characterization of planarized multilayer atom chips with enhanced heat dissipation

This paper describes the design and fabrication of planarized multilayer atom chips for an ultrahigh-vacuum system in atomic physics experiments. A fabrication process is developed to define micrometer-scale wire patterns on a silicon substrate and wires are plated by copper electroplating. SU-8 is chosen as the isolation layer between the upper and bottom wires, and its thickness, surface flatness and surface roughness (Ra = 5 nm) are controlled by the chemical–mechanical planarization process. A reflectivity of nearly 90% is measured on the chip surface; thus, the former method of attaching a silver mirror is unnecessary (Du et al 2004 Phys. Rev. A 70 053606). A heat dissipation copper block is incorporated in our chip design to increase the sustainable current densities of upper wires of more than 3.8 × 105 A cm−2. Results show the improvement of 55.74%, compared with the nonheat dissipation design (2.44 × 105 A cm−2), and thus meeting the requirements for chip-based atom trapping experiments.

Tunable external cavity diode laser using a micromachined silicon flexure and a volume holographic reflection grating for applications in atomic optics

We present a novel external cavity diode laser design devel- oped for applications in atomic physics that employs a micromachined silicon flexure to sweep the laser frequency and a volume holographic reflection grating VHG to provide the optical feedback. The advantages of using a silicon flexure are its simple microfabrication process and reduction of the overall size of the laser system. The results demonstrate the 87 Rb, 85 Rb rubidium D2 line absorption at 780 nm in an atomic optics test experiment. Our novel laser system design has a size of 28.7620.6512 mm. The wavelength can be tuned and swept from 780.2463 to 780.2379 nm equivalent to 4.14 GHz using piezoelectric transducer PZT actuators integrated on the silicon flexure. A frequency tuning range of 17.149 GHz can be obtained by changing the VHG tem- perature. The deflection of the silicon flexure is 129.19 nm. The advan- tage of combining a VHG and a silicon flexure is that the frequency can be coarsely tuned to 780.24 nm and swept at this center frequency with a range of 4.14 GHz by PZT. Moreover, the frequency fine tuning can be achieved by changing the VHG temperature to observe the rubidium spectrum. The laser output power is measured as 59 mW at 780.2474 nm.

Verification and compensation of respiratory motion using an ultrasound imaging system

PURPOSE The purpose of this study was to determine if it is feasible to use ultrasound imaging as an aid for moving the treatment couch during diagnosis and treatment procedures associated with radiation therapy, in order to offset organ displacement caused by respiratory motion. A noninvasive ultrasound system was used to replace the C-arm device during diagnosis and treatment with the aims of reducing the x-ray radiation dose on the human body while simultaneously being able to monitor organ displacements. METHODS This study used a proposed respiratory compensating system combined with an ultrasound imaging system to monitor the compensation effect of respiratory motion. The accuracy of the compensation effect was verified by fluoroscopy, which means that fluoroscopy could be replaced so as to reduce unnecessary radiation dose on patients. A respiratory simulation system was used to simulate the respiratory motion of the human abdomen and a strain gauge (respiratory signal acquisition device) was used to capture the simulated respiratory signals. The target displacements could be detected by an ultrasound probe and used as a reference for adjusting the gain value of the respiratory signal used by the respiratory compensating system. This ensured that the amplitude of the respiratory compensation signal was a faithful representation of the target displacement. RESULTS The results show that performing respiratory compensation with the assistance of the ultrasound images reduced the compensation error of the respiratory compensating system to 0.81-2.92 mm, both for sine-wave input signals with amplitudes of 5, 10, and 15 mm, and human respiratory signals; this represented compensation of the respiratory motion by up to 92.48%. In addition, the respiratory signals of 10 patients were captured in clinical trials, while their diaphragm displacements were observed simultaneously using ultrasound. Using the respiratory compensating system to offset, the diaphragm displacement resulted in compensation rates of 60%-84.4%. CONCLUSIONS This study has shown that a respiratory compensating system combined with noninvasive ultrasound can provide real-time compensation of the respiratory motion of patients.