Lubomyr T. Romankiw

A 2.5D Integrated Voltage Regulator Using Coupled-Magnetic-Core Inductors on Silicon Interposer

An integrated voltage regulator (IVR) is presented that uses custom fabricated thin-film magnetic power inductors. The inductors are fabricated on a silicon interposer and integrated with a multi-phase buck converter IC by 2.5D chip stacking. Several inductor design variations have been fabricated and tested. The best performance has been achieved with a set of eight coupled inductors that each occupies 0.245 mm2 and provides 12.5 nH with 270 mΩ DC. With early inductor prototypes, the IVR efficiency for a 1.8 V:1.0 V conversion ratio peaks at 71% with FEOL current density of 10.8 A/mm2 and inductor current density of 1.53 A/mm2. At maximum load current, 69% conversion efficiency and 1.8 V:1.2 V conversion ratio the FEOL current density reaches 22.6 A/mm2 and inductor current density reaches 3.21 A/mm2.

The Influence of Lithographic Patterning on Current Distribution: A Model for Microfabrication by Electrodeposition

A model has been developed to predict current distribution in electrodeposition onto substrates that contain lithographic patterns. The aim of the work was to understand the strong effects that substrate patterning can exert on the thickness distribution of plated films. Based on the familiar potential‐theory model for secondary current distribution in electrochemical cells, the model is applicable at length scales that are large compared to the individual features of a pattern. The pattern is described entirely as a continuous distribution of active‐area density, a property that reflects any relative change in the electroactive area of the substrate due to the pattern. The active‐area density enters the expression that relates the surface overpotential to the current density. An implementation of the model, using the boundary‐element method, has been applied to several problems that illustrate the effects of substrate patterning on current distribution. For each example, the dimensionless groups that characterize the current distribution have been identified, general solutions have been obtained over wide parameter ranges, and behavioral trends have been interpreted.

In situ surface pH measurement during electrolysis using a rotating pH electrode

An in situ technique has been developed for measuring the surface pH adjacent to a solid electrode/liquid interface during electrolysis. Measurements of the surface pH can be used to obtain insights regarding the electrodeposition of various transition metals and to obtain a better understanding of associated in situ surface chemistry effects. Many transition metals and alloys deposit with simultaneous hydrogen evolution and, as a result, are accompanied by a pH rise near the cathode, thereby affecting the reactivity of the nearby metal-ion species. Measurements of the surface pH of a solution containing simple salts during hydrogen evolution from a cathode were performed. The surface pH of a cathode during Ni and NiFe electrodeposition was also measured. The experiments demonstrated that, in the absence of buffers or metal ions, the surface pH rises many pH units above the bulk value. During Ni and NiFe electrodeposition, however, the surface pH of solutions consisting of simple salts and starting from a bulk pH level of 2 does not increase more than 3 pH units from the bulk value. In the case of Ni and NiFe electrodeposition, surface buffering occurs because of the hydrolysis of the metal-ion species present. Additionally, it is found that during the anomalous codeposition of NiFe, the surface pH is much lower than that required by the Dahms-Croll hypothesis.

Optimization of Electrodeposit Uniformity by the Use of Auxiliary Electrodes

Un modele numerique est utilise pour examiner comment luniformite de la distribution du courant sur une electrode plane peut etre amelioree en utilisant une electrode auxiliaire coplanaire

Pulsed Potentiostatic Deposition of Gold from Solutions of the Au(I) Sulfite Complex

The kinetics of Au deposition from Au(I) sulfite solutions in the pH range 8.5–13 has been studied using cyclic voltammetry and single potential step methods. At potentials more positive than −0.8V vs. NHE, the potential step data can be explained by a C.E. mechanism, probably dissociation of the gold complex followed by charge transfer. At more cathodic potentials the mechanism may involve direct electron transfer to the complexed gold ion. The effect of pulsed potentiostatic deposition on the properties of Au films deposited from sulfite solutions was investigated. Although variation of the frequency of the potential pulse was shown to affect the distribution of Au deposited through a photoresist pattern, the stress, grain size, purity, and resistivity of gold deposited pulsed potentiostatically showed no clear dependence on frequency. This can be explained in terms of irreversibility of the Au/Au(I) couple in sulfite solution.

Electrochemical process for advanced package fabrication

Interconnections for high-end applications are essentially low-resistance transmission-line structures with precisely controlled cross-sectional shapes and dimensions. The relatively thick copper conductors-typically 6 µm or more-combined with the stringent control required on the 10-20-µm-wide cross sections stretches the capabilities of the subtractive etch and lift-off processes that are typically used in semiconductor fabrication to pattern evaporated and sputtered metal films. Electroplating through a photoresist mask, which has proven itself to be a highly effective, precision manufacturing process for thin-film magnetic recording heads, is, however, capable of meeting and far exceeding the requirements of package fabrication. This paper describes the fabrication of a package structure that integrates traditional dry-process technologies with electrolytic copper plating to form the conductors, polyimide backfill and planarization steps to form the dielectric, and electroless deposition to selectively clad the copper lines to prevent adverse reaction of the copper with water generated during the polyimide cure. The discussion highlights salient issues which are pertinent to the compatibility of the individual process steps and to the extension of the technology to more demanding packaging structures and to other applications.

A TEM Study of the Effect of Accelerators on Pd‐Sn Colloidal Catalysts and on the Initiation of Electroless Cu Deposition on Epoxy

Etude de lactivation superficielle de lepoxy et de linitiation du processus de depot du Cu. Mesures par EDX de la composition des particules nucleees de Cu. Determination des etapes dactivation avec le catalyseur Pd−Sn et etude de linfluence des accelerateurs NaOH, HCl et EDTA

A 2.5D integrated voltage regulator using coupled-magnetic-core inductors on silicon interposer delivering 10.8A/mm 2

Energy consumption is a dominant constraint on the performance of modern microprocessors and systems-on-chip. Dynamic voltage and frequency scaling (DVFS) is a promising technique for performing “on-the-fly” energy-performance optimization in the presence of workload variability. Effective implementation of DVFS requires voltage regulators that can provide many independent power supplies and can transition power supply levels on nanosecond timescales, which is not possible with modern board-level voltage regulator modules (VRMs) [1]. Switched-inductor integrated voltage regulators (IVRs) can enable effective implementation of DVFS, eliminating the need for separate VRMs and reducing power distribution network (PDN) impedance requirements by performing dc-dc conversion close to the load while supporting high peak current densities [2–3]. The primary obstacle facing development of IVRs is integration of suitable power inductors. This work presents an early prototype switched-inductor IVR using 2.5D chip stacking for inductor integration.

Integrated, variable-reluctance magnetic minimotor

The use of lithography and electroplating to fabricate variable-reluctance, nearly planar, integrated minimotors with 6-mm-diameter rotors on silicon wafers is described. The motors consist of six electroplated Permalloy® horseshoe-shaped cores that surround the rotor. Copper coils are formed around each core. The Permalloy and copper electroplating baths, electroplating seed layers, and through-mask plating techniques are similar to those used to fabricate inductive thin-film heads. High-aspect-ratio optical lithography or X-ray lithography was used to form the various resist layers. The rotors were fabricated separately, released from the substrate, and then slipped onto the shaft, which was plated as part of the stator fabrication process. The fabrication processes for stator and rotor are described in this paper, and initial minimotor operation data are presented.

Liquid magnetic bubbles

A liquid analog of a magnetic bubble domain shift register has been constructed, using ferrofluid and an immiscible liquid. Bubble sizes from 50 to 1000 microns have been observed, with propagation frequencies to 60 Hz and propagation velocities for 300 micron bubbles of up to 6 cm/ sec. Display applications for these phenomena are discussed.