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- Hsu, Li-Han, 1981
(författare)
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Flip-Chip Interconnect for Millimeter-Wave Packaging Applications
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, with the demands for wireless communication systems increas rapidly, the operating frequency for the portable wireless is moving toward millimeter-waves. Millimeter-wave wireless communication systems require not only suitable functional IC components but also competent package with low cost and good interconnect performance. To meet the demands for commercial applications, package with low power consumption, low cost, small size, and light weight becomes indispensable. However, unlike low frequency applications, millimeter-wave frequencies introduce significant parasitics and therefore the interconnect between IC chips and packaging carriers must be carefully managed in order to maintain good electrical performance. Conventional bond-wire induces significant parasitic inductance and thus results in unwanted effects, which could deviate the IC performance after assembly, especially at millimeter-wave frequencies.Flip-chip interconnect has drawn lots of attentions for chip-level packaging at millimeter-wave frequencies due to several advantages over bond-wire, e.g., shorter interconnect length, smaller package size and higher throughput. However, at MMW frequency range, the proximity effect, or detuning effect, is a crucial issue for flip-chip due to the proximity of chip to substrate. The proximity effect may cause the flipped-chips to deviate from its original performance. Approaches like increasing the bump height, reducing the metal overlap and employing compensation design at the transition region have been proposed to improve flip-chip performance. In addition, flip- chip reliability is very crucial for industrial applications since it relies only on several metallic connections. Using underfill as a buffer layer between chips and carriers can significantly improve flip-chip reliability, but unfortunately, the trade-off is underfill-induced performance decay and deviation. Furthermore, cost-reduction is also very important for commercialization. Conventional ceramic-based carrier offers excellent chemical and physical properties but with higher cost. Using low-cost organic board might be a good solution to get lower cost with fair performance. However, the investigation for flip-chip on organic board is generally insufficient.This dissertation covers an overall study for flip-chip interconnect for millimeter-wave frequencies. It can be divided into two parts. The first part is about active device packaging. Single MMIC chips and mm-wave modules were flip-chip assembled for demonstration. A V-band SPDT switch for half-duplex RF front-end switching was flip-chip assembled and RF characterized to 67 GHz. By adopting hi-compensation design, the packaged switch showed excellent frequency response and very low additional loss.Moreover, a V-band frequency source with a 7 GHz oscillator and a x8 multiplier was flip-chip assembled onto a multi-chip carrier. For comparison, both the oscillator and x8 multiplier were also bonded as individual chips. From the measurement results, the flip-chip technique did not have any detrimental effects and the assembled module showed excellent phase noise of -112 dBc/Hz @ 1 MHz offset with high output power of 11 dBm, demonstrating outstanding performance for millimeter-wave frequency generation.The second part is about material investigation in a flip-chip system. Underfill is generally required for improving flip-chip reliability. However, underfill in a flip-chip interconnect might introduce negative effects i.e., chip impedance mismatch and dielectric loss at millimeter-wave frequencies. To investigate and solve this issue, an epoxy-based was applied to a flip-chip structure and measured up to 67 GHz. By using pre-matching design and low-loss underfill, the flip-chip assembly exhibited excellent performances with return loss below -20 dB and insertion loss less than 0.6 dB. In addition, the reliability test revealed that the flip-chip assembly also performed excellent reliability. The other material investigation is about flip-chip carrier material. Low-cost Rogers RO3210TM organic laminate was employed to replace ceramic-based carrier for cost reduction and performance improvement. Both passive transmission lines and active discrete mHEMTs were flip-chip bonded onto RO3210TM. The test results showed that RO3210TM is a promising packaging carrier for commercial applications up to 50 GHz.
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| 2. |
- Hsu, Li-Ju
(författare)
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Neuronal mechanisms of feedback postural control
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Different species maintain a basic body posture due to the activity of the postural control system. An efficient control of the body orientation, as well as the body configuration, is important for standing and during locomotion. A general goal of the present study was to analyze neuronal feedback mechanisms contributing to stabilization of the trunk orientation in space, as well as those controlling the body configuration. Two animal models of different complexity, the lamprey (a lower vertebrate) and the rabbit (a mammal), were used. Neuronal mechanisms underlying lateral stability were analyzed in rabbits. The dorsalside- up trunk orientation in standing quadrupeds is maintained by the postural system driven mainly by somatosensory inputs from the limbs. Postural limb reflexes (PLRs) represent a substantial component of this system. To characterize spinal neurons of the postural networks, in decerebrate rabbit, activity of individual spinal neurons in L4-L6 was recorded during PLRs caused by lateral tilts of the supporting platform. Spinal neurons mediating PLRs have been revealed, and different parameters of their activity were characterized. All neurons were classified into four types according to the combination of tilt-related sensory inputs to a neuron from the ipsi- and contralateral limb (determining the modulation of a neuron). A hypothesis about the role of different types of PLR-related neurons for trunk stabilization in different planes has been proposed. To reveal contribution of supraspinal influences to modulation of PLR-related neurons, the activity of individual spinal neurons was recorded during stimulation causing PLRs under two conditions: (i) when spinal neurons received supraspinal influences, and (ii) when these influences were temporarily abolished by a cold block of spike propagation in spinal pathways at T12 (“reversible spinalization”). The effects of reversible spinalization on individual neurons were diverse. Neurons, which did not receive supraspinal influences, were located mainly in the dorsal horn, whereas most neurons, receiving excitatory supraspinal influences were located in the intermediate zone and ventral horn. The population of PLRrelated neurons presumably responsible for disappearance of muscle tone and PLRs after spinalization was revealed. The effects of manipulation with the tonic supraspinal drive (by means of binaural galvanic vestibular stimulation, GVS) on the postural system were studied. GVS creates asymmetry in tonic supraspinal drive, resulting in a lateral body sway towards the anode. This new body orientation is actively stabilized. To reveal the underlying mechanisms, spinal neurons were recorded during PLRs with and without GVS. It was found that GVS enhanced PLRs on the cathode side and reduced them on the anode side. It was suggested that GVS changes the set-point of the postural system through the change of the gain in antagonistic PLRs. Two sub-groups of PLR-related neurons presumably mediating the effect of GVS on PLRs were found. An artificial feedback system was formed in which GVS-caused body sway was used to counteract the lateral body sway resulting from a mechanical perturbation of posture. It was demonstrated that the GVS-based artificial feedback was able to restore the postural function in rabbits with postural deficit. We suggested that such a control system could compensate for the loss of lateral stability of different etiology. Neuronal mechanisms underlying control of body configuration were analyzed in lampreys. The lamprey is capable of different forms of motor behavior: fast forward swimming (FFS), slow forward swimming (SFS), backward swimming (BS), forward and backward crawling, and lateral turns (LT). The amplitude of the body flexion (characterizing the body configuration) differs in different forms of motor behavior. In the lamprey, signals about the body configuration are provided by intraspinal stretch receptor neurons (SRNs). To clarify whether the networks generating different forms of motor behavior are located in the spinal cord, in chronic spinal lampreys, electrical stimulation of the spinal cord was performed. It was demonstrated that all forms of motor behavior are generated by the spinal networks. To study SRN-mediated reflexes and their contribution to the control of body configuration in different motor behaviors, in the in vitro preparation we recorded responses of reticulospinal (RS) neurons and motoneurons (MNs) to bending of the spinal cord in different planes and at different rostro-caudal levels during different forms of fictive motor behavior Bending in the pitch plane during FFS caused SRN-mediated reflexes. MNs on the convex side were activated by pitch bending in the mid-body region. These reflexes will reduce the bend, thus contributing to maintenance of rectilinear body axis in the pitch plane during FFS. It was found that bending in the yaw plane activated MNs on the convex side during FFS, but on the concave side during different forms of escape behavior (SFS, BS, LT). It was demonstrated that a reversal of reflex responses was due to ipsilateral supraspinal commands causing modifications of the spinal network located in the ipsi-hemicord. A population of RS neurons (residing in the middle rhombencephalic reticular nuclei) presumably transmitting these commands has been revealed. We suggest that modifications of SRN-mediated reflex responses will result in the decrease and increase of the lateral bending amplitude during FFS and escape behaviors, respectively, thus reinforcing movements generated in each specific behavior. Thus in the present study, for the first time, some neuronal mechanisms underlying reflex reversal in vertebrate animals have been revealed.
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