Noah Sturcken

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.

Integrated on-chip inductors with electroplated magnetic yokes (invited)

Thin-film ferromagnetic inductors show great potential as the energy storage element for integrated circuits containing on-chip power management. In order to achieve the high energy storage required for power management, on-chip inductors require relatively thick magnetic yoke materials (several microns or more), which can be readily deposited by electroplating through a photoresist mask as demonstrated in this paper, the yoke material of choice being Ni45Fe55, whose properties of relatively high moment and electrical resistivity make it an attractive model yoke material for inductors. Inductors were designed with a variety of yoke geometries, and included both single-turn and multi-turn coil designs, which were fabricated on 200 mm silicon wafers in a CMOS back-end-of-line (BEOL) facility. Each inductor consisted of electroplated copper coils enclosed by the electroplated Ni45Fe55 yokes; aspects of the fabrication of the inductors are discussed. Magnetic properties of the electroplated yoke materials are...

Design of coupled power inductors with crossed anisotropy magnetic core for integrated power conversion

Design and partial microfabrication of a coupled power inductor is presented for use in high power-density integrated voltage regulators (IVR). The proposed inductor uses many laminations of uniaxial, high-permeability magnetic material where the orientation of anisotropy between successive laminations is rotated to provide an effectively isotropic core. The high permeability core allows for an inductance density of 200nH/mm2, while coupling between phases prevents magnetic saturation and allows a current density as high as 11A/mm2 according to quasi-static finite-element-analysis (FEA) simulations. The coupling factor, inductance and resistance of the device are optimized for operation in a four-phase integrated buck converter switching at 100MHz.

A Switched-Inductor Integrated Voltage Regulator With Nonlinear Feedback and Network-on-Chip Load in 45 nm SOI

A four-phase integrated buck converter in 45 nm silicon-on-insulator (SOI) technology is presented. The controller uses unlatched pulse-width modulation (PWM) with nonlinear gain to provide both stable small-signal dynamics and fast response (~700 ps) to large input and output transients. This fast control approach reduces the required output capacitance by 5× in comparison to a conventional, latched PWM controller at a similar operating point. The converter switches package-integrated air-core inductors at 80 MHz and delivers 1 A/mm2 at 83% efficiency and 0.66 conversion ratio. A network-on-chip (NoC) serves as a realistic digital load along with a programmable current source capable of generating load current steps with slew rate of ~1 A/100 ps for characterization of the control scheme.

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.

Magnetic thin-film inductors for monolithic integration with CMOS

This paper presents the fabrication, design and electrical performance of magnetic thin-film inductors for monolithic integration with CMOS for DC-DC power conversion. Magnetic core inductors were fabricated using conventional CMOS processes to achieve peak inductance density of 290nH/mm2, quality factor 15 at 150MHz, current density exceeding 11 A/mm2 and coupling coefficient of 0.89 for coupled inductors.

Vector control of induced magnetic anisotropy using an in situ quadrupole electromagnet in ultrahigh vacuum sputtering

We demonstrate the incorporation of a quadrupole electromagnet into an ultrahigh vacuum sputtering system for the vector control of induced magnetic anisotropy in magnetic thin-film heterostructures. A stationary quadrupole electromagnet is used to generate a magnetic field, which rotates synchronously with the physical axes of the substrate in situ during sputtering. An arbitrary anisotropy direction can be set for successive ferromagnetic layers by adjusting the phase difference of substrate and field rotation. The ability to rotate the substrate during deposition and change anisotropy without breaking vacuum enables the deposition of magnetically soft heterostructures with arbitrary in-plane anisotropy axes.

An integrated four-phase buck converter delivering 1A/mm 2 with 700ps controller delay and network-on-chip load in 45-nm SOI

We present a four-phase integrated buck converter in 45nm SOI technology. The controller uses unlatched pulse-width modulation (PWM) with nonlinear gain to provide both stable small-signal dynamics and fast response (∼700ps) to large input and output transients. This fast control approach reduces the required output capacitance by 5X in comparison to a controller with latched PWM at similar operating point. The converter switches at 80MHz and delivers 1A/mm2 at 83% efficiency and 0.66 conversion ratio.

Coupled Inductors With Crossed Anisotropy

Four-turn coupled (flux-closed) inductor structures have been fabricated and tested for use in high-power-density integrated voltage regulator (IVR) applications. Our solenoid-like structure is comprised of a laminated magnetic core of four rungs surrounded by four Cu windings creating four coupled inductors. The magnetic core is made of laminations of ultra-high-vacuum-sputtered [5 nm Ta/200 nm Co91.5Zr4.0Ta4.5(CZT)/7 nm SiO2] repeated 20 times. Individual CZT layers are deposited under a magnetic bias to induce uniaxial anisotropy. The quad-coupled inductor shows a frequency response with a measured self-inductance of 7.4 nH for one inductor sustained up to 100 MHz and roll-off to half this low-frequency value at ~450 MHz. This inductance is more than 65× higher than what would be calculated from an air-core inductor of equivalent geometry.

{\rm CoZrTa/SiO}_{2}

This paper presents a three-dimensional (3D) fully integrated high-speed multiphase voltage regulator. A complete switched-inductor regulator is integrated with a four-plane NoC in a two-high chip stack combining integrated magnetics, through-silicon vias (TSVs), and 45-nm SOI CMOS devices. Quasi-V2 hysteretic control is implemented over eight injection-locked fixed-frequency phases to achieve fast response, steady-state regulation, and fixed switching frequency. Peak efficiency of 82% for conversion from 1.66 V to 0.83 V is observed at a 150 MHz per-phase switching frequency. This is the first demonstration of high-speed voltage regulation using on-chip magnetic-core inductors in a 3D stack and achieves sub-μs dynamic supply voltage scaling for high-density embedded processing applications.