Zihan Wu

Magnetic Materials and Design Trade-Offs for High Inductance Density, High-Q and Low-Cost Power and EMI Filter Inductors

This paper investigates the trade-offs in inductance density and quality factor of inductors with and without magnetic-cores through modeling, design, fabrication and model validation through characterization. Two type of inductors, one for power-supply and the other for EMI filters, are investigated. Parametric analysis was performed to study the enhancement in inductance density without compromising the current handling and efficiency. For EMI filter inductors, the inductance and quality factor (Q) were improved by 13X and 4X respectively with and without magnetic cores. For power inductors, the inductance and quality factor were improved by 5X and 1.6X respectively. The fabricated magnetic core inductors achieved 5X reduction in thickness, compared to the stage-of-the art air-core inductors which use multilayered and thick solenoid.

Design and Demonstration of Ultra-Thin Glass 3D IPD Diplexers

This paper demonstrates, for the first time, 3D integrated passive device (IPD) diplexers on ultra-thin glass substrates for wireless local area network (WLAN) application in mobile devices. The designed LC-based diplexer was composed of a low-band filter and a high-band filter, built on ultra-thin glass substrates. The two filters were designed on each side of the glass substrate and interconnected by through-package-vias (TPVs) to form a 3D IPD. Ultra-thin and low-loss dryfilm dielectrics were utilized for improved electrical performance as well as to achieve high-density of passives integration. The demonstrated 3D IPD diplexer is 3-4X thinner than current LTCC devices, with lateral dimensions of 1.1mm x 1.3mm in a thickness of 200μm resulting in a low insertion loss of less than 1dB for pass bands and more than 24dB stop-band rejection.

Innovative Electrical Thermal Co-Design of Ultra-High Q TPV-Based 3D Inductors in Glass Packages

This paper introduces an innovative concept of electrical-thermal co-design for high-Q 3D inductors using through-package-via (TPV)-based copper networks in ultra-thin power amplifier-integrated glass modules. The copper networks are designed to provide high quality factor inductors, and also simultaneously enable heat transfer in ultra-miniaturized glass packages. Such TPV-based 3D inductors achieved the highest Q factor (>150 @ 1 GHz, >200 @ 2.4 GHz, SRF > 25 GHz), 7 times greater than that of the state-of-the-art package embedded inductors at LTE frequencies. The thermal structure, with power amplifier die assembled onto it, also reduces the package size by placing the embedded TPV-based inductor adjacent to it without affecting its Q.

Modeling Design Fabrication and Demonstration of RF Front-End Module with Ultra-Thin Glass Substrate for LTE Applications

This paper demonstrates, for the first time, an integrated radio frequency (RF) front-end module (FEM) with precision matching circuits in ultra-miniaturized glass substrates for LTE applications. Through full-wave electromagnetic (EM) simulations, electrical performance of these glass-based long term evolution (LTE) packages is compared with traditional RF modules with surface mount devices (SMDs), and organic laminates with embedded passives and actives. RF front-end modules with 3D or double-side thin film passive components on glass-based substrates are fabricated and characterized to correlate their performance with EM simulations.

3D printed wearable flexible SIW and microfluidics sensors for Internet of Things and smart health applications

In this paper, a flexible SIW wearable sensing platform is proposed with a novel 3D printing process which enables fast-prototyping customized wearable devices. The fabrication utilizes state-of-the-art SLA 3D printing that features fast prototyping of easy-to-reconfigure flexible 3D objects. Two different flexible metallization approaches are explored in this paper, which are complementary to each other and provide an excellent 3D metallization solution together. Two 3D shape SIW transmission lines are shown with a great flexibility and great potential for wearable devices. Moreover, based on a SIW slot waveguide antenna, this paper presents a proof-of-concept microfluidics sensor with sensitivity of 1.7 MHz/Er, which can be used as a wearable sensing device for real-time monitoring of body fluids. The proposed SIW-based flexible wearable devices along with the microfluidics sensors can be used in various Internet-of-Things applications, such as smart health and food quality monitoring.

Modeling, design and fabrication of ultra-thin and low CTE organic interposers at 40µm I/O pitch

This paper presents a comprehensive study on the fundamental factors that impact the scalability of organic interposers to 40μm area array bump pitch, leading to the design and fabrication of ultra-thin and low CTE organic interposers at 40μm pitch. Silicon interposers were the first substrates used for 2.5D integration of logic and memory ICs at close proximity. However, the high cost and electrical loss of wafer back end of line (BEOL) silicon interposers has fueled the need for fine-pitch organic interposers. Organic substrates face two primary challenges in achieving finer I/O pitch: layer-to-layer mis-registration during copper-polymer re-distribution layer (RDL) fabrication due to the thermo-mechanical stability issue of organic laminate cores, and warpage during chip assembly on thin core substrates. This paper studies these two fundamental factors by finite element modeling (FEM) and experimental characterization, resulting in RDL design guidelines for low mis-registration and warpage. Reducing the copper thickness in each layer as well as the thickness of the polymer dielectric to below 10μm, resulted in significant reduction in CTE mismatch-induced stresses at different interfaces. The modeling-based design was verified by fabrication of a multi-layer RDL stack on 100μm thin low coefficient of thermal expansion (CTE) organic cores with ultra-thin build-up layers to achieve a bump pitch of 40μm. The assembly of chips on the thin organic interposer was optimized to minimize the warpage, leading to the demonstration of two-chip 2.5D organic interposers.

Design and demonstration of paper-thin and low-warpage single and 3D organic packages with chip-last embedding technology for smart mobile applications

This paper presents innovations and advances in demonstrating paper-thin organic packages with low warpage. These advances include: 1) Reduction in over-all substrate warpage, 2) Ultra-low stand off interconnection height, 3) Ultra-thin (30 μm core thickness) and ultra-low CTE (1-5 ppm/°C) organic substrates, 4) Assembly of large die onto the ultra-thin substrate, and 5) Assembly to form advanced package-on-package using conventional batch-type SMT reflow processes. Design, fabrication, assembly and characterization of test-vehicles demonstrating all these innovations are described in this paper. Comprehensive warpage modeling is performed by taking into account all substrate fabrication and assembly steps. The measured warpage data after package fabrication and assembly was used to refine and validate the models. Optimized geometry and material parameters are designed from the validated models.