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Reconfigurable mm Wave Flexible Packages with Ultra-thin Fan-Out Embedded Tunable Ceramic IPDs
Keywords: reconfigurable, mm wave, tunable IPDs
Heterogeneous integration technologies are the key to realize future high- bandwidth communication systems with enhanced mobile broadband and massive IoT connectivity, implantable and wearables for health monitoring and therapy, Autonomous Driver Assistance Systems (ADAS) and others. Limited bandwidth in S and C band is compelling users to utilize mm wave bands with superior spectral efficiency, spatial multiplexing and concurrent beams. Future 5G solutions require RF communication interfaces that are smart and reconfigurable based on ambient RF conditions and traffic. Reconfigurability with seamless switching between broadbands is a key challenge in realizing such systems. With regards to mm-wave 5G communication, two foundational challenges among beam-steering arrays have been the ability to provide a range of phase-shift as well as low- loss distribution network. Ability of flexible substrates for wearable reconfigurable devices is another area, which has become crucial with advent of millimeter wave and internet of things devices. Embedding of passive components with active devices in fan- out antenna-integrated packages will emerge as prevalent technology to realize this. Flexible polymer carriers, low-loss laminates and glass are emerged as key substrate candidates. However, the functional density integration is limited with these substrate options. Certain functions such as reconfigurability with miniaturized feeding networks are ideally integrated in thin ceramic devices (IPDs) and then fan-out embedded into the antenna-integrated laminate or flexible packages. This allows density and functionality in the ceramic islands that are then seamlessly connected to the substrates. This hybrid approach is the key to future mm wave SiPs. Ultra-thin ceramic integrated passive devices are thus expected to provide next evolutionary solution for flexible and wearable communication devices by providing low- loss as well as reconfigurability and could enable a generation of smart wearable devices. The paper will demonstrate the application of tunable capacitors for realizing phase shifters for RF applications. A target frequency band of consideration is 10-20 GHz and possible extrapolation up to popular millimeter wave bands of 28 and 38 GHz will be considered. Ceramic thinfilms of barium strontium titanate will be deposited onto ceramic IPD carriers and embedded into flexible packages. The first step is to ensure ultra- smooth surfaces so that defect-free films can be deposited. Thin ceramic carriers were obtained from our proprietary partners. Thin lanthanum nickel oxide was RF sputter-deposited onto the substrates. This was followed by RF sputtering of barium strontium titanate, followed by annealing at 700 C for 1 hr to crystallize the nanocrystalline perovskite phase. Thin copper was evaporated onto the top to act as the top electrode. Tunability of 3-4X at bias voltages of 3-5 V is shown. The RF performance in reconfigurable feeding networks will be shown with a tunable-capacitors inside the feeding network. Reconfigurability of 3:1 with low insertion losses is projected from the deposited films. The first part of the analysis is to investigate and establish the utility of embedded ceramic thinfilms of barium strontium titanate on ceramic carriers for microwave and millimeter applications, specially so with antenna applications. Antenna configurations under study will be upto 16 element antenna using serial and corporate feed network where tunable capacitors will be used to create the required phase shift for beam steering. The specific plane for experimentation and sherardization includes testing of capacitor values by introducing them into packaged transmission lines and measurement of capacitance using one port and two port measurements. De- embedding methods will be used to calculate the real and imaginary part of impedance over a wide range of frequencies providing for capacitance as well as resistance values. These will be used to make capacitor models to be used for circuit design for phase-shifters and filters. These will be considered keeping in mind the requirement for phase-shifters for beam-steering applications. Parallel and series resonant circuits will be considered for enabling the required phase shifts based on values obtained from the basic characterization plan outlined above. An important part of experimentation and characterization will be to estimate available values and learn the range of tunability for achieving the specs needed for the said applications. Characterization results for capacitors, and their simulated performance in series/parallel LC based phase-shifters and for their losses and phase shifting abilities will be presented and discussed. The RF performance in reconfigurable feeding networks will be shown with a tunable- capacitors inside the feeding network. Reconfigurability of 3:1 with low insertion losses is projected from the deposited films. The second analysis of the developed tunable capacitor technology will be in tunable filters and antenna matching components for frequency reconfigurability and developing notch filters as an interference deterrent. Such notch filters are required for applications where frequency of a jammer is recognized in-situ and a notch filter can be reconfigured to block such frequency to protect saturation of analogue front-end chain. This passive anti-jamming is critical to many low-power RF communication applications, specially at millimeter wave frequencies where circuits are miniaturized, and Si-based solutions are lossy.
Shubhendu Bhardwaj, Associate Professor
Florida International University
Miami, FL

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