Philipp Herget

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...

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.

A Study of Current Density Limits Due to Saturation in Thin Film Magnetic Inductors for On-Chip Power Conversion

Saturation in thin film coupled magnetic inductors was measured as a function of dc current in both windings. A simple mathematical model was created to approximate the inductor saturation level in the presence of the two currents. The model was compared both to FEM calculations of saturation in a linear model and to the experimental findings. Using the mathematical model, an expression for the maximum dc current and maximum flux levels in the yokes was derived for a two phase coupled buck converter, as a function of coupling.

Limits to On-Chip Power Conversion With Thin Film Inductors

Successful implementation of on-chip power conversion using ferromagnetic inductors requires both high power efficiency and high power density. The theoretical limits to power density and efficiency possible with thin film ferromagnetic inductors in a buck converter topology with and without coupling are explored. Power density can be related to energy density of the inductor, while efficiency can be related to Q and the DC resistance loss of the inductor. To achieve 100 A/cm2 for a 100 MHz 2:1 V converter with a 90% inductor efficiency, a peak Q of more than 8 is required with an energy storage of more than 5 nJ/mm2. Using coupling, the power density can be further increased, but is ultimately limited by DC resistance loss in the coils. Figures of merit (FOM) for comparing inductors of various designs are also discussed.

Laser Diode Active Height Control for Near Field Optical Storage

The use of commercial laser diodes as near field, nano-scale position sensors for feedback control systems was experimentally investigated. A static experimental setup was constructed to measure and characterize the laser diode feedback mechanism. Experiments show that the lasers, which act as miniature interferometers, provide a high accuracy, high signal-to-noise ratio (SNR) signal both in the near and far field. The laser diodes were then mounted in commercial digital versatile disc (DVD) actuators and a control system was constructed. The control system can operate both in the near and far field, and a controlled approach from the far to near field is demonstrated using a fringe jump controller. Finally, using the experimentally gathered feedback data, the residual control error of ±1 nm was estimated for this system.

Tunable diode protection for GMR and TMR sensors

TMR and GMR sensors used today are highly susceptible to ESD damage with failure voltages as low as 0.5 V. Diode protection using a single diode connected in parallel with the sensor does not work for many advanced MR sensors due to the fact that the voltage at which diodes begin conducting significant current exceeds the damage voltage of many advanced MR sensors. This is due to limitations of the band gaps of the diode materials (Si and Ge) and the resistance of the diodes while conducting. Here we report several novel diode protection circuits which enable protecting the most sensitive devices while tuning the circuits to the electrical characteristics of the particular sensor being used.

Optical Feedback Height Control System Using Laser Diode Sensor for Near-Field Data Storage Applications

We demonstrated a laser diode position sensor for a near-field height control system. The feedback signal of the laser diode sensor that resulted from self-mixing interferometry was characterized and modeled by a simplified method. Due to the fine spatial resolution of the laser sensor, an active height control system with nanoscale position precision was designed and realized under a spinning disk for near-field applications.

Planar Thin-Film Servo Write Head for Magnetic Tape Recording

We present a planar thin-film servo write head for writing timing-based servo patterns. The planar head operates at low current ( ~ 100 mA) with nanosecond switching times. The planar head can handle dc current, enabling trailing-edge writing. Magnetic force microscopy measurements of the transitions written by the planar head and a conventional commercial servo write head on longitudinal metal particle and nonoriented barium ferrite media were made to assess the quality of the written transitions. The transition response width PW50 is found to be independent of the tape velocity during write for the planar head. For the conventional head, PW50 is larger and increases with the tape write velocity. The reduced PW50 results in larger readback signal amplitude and hence an improved track-follow performance. The faster switching capability of the planar head enables formatting at higher tape velocity.

Mark shapes in hybrid recording

We describe the theoretical and experimental investigation of mark shapes in thermally assisted or hybrid recording. The effect of alignment was studied by recording marks on perpendicular TbFeCo media using a commercial recording head and 840 nm laser. We found that mark shapes are primarily controlled through laser/head alignment, and that maximally straight transitions are obtained by placing the laser spot on the leading pole tip near the gap. Simulations of the recording process confirm the experimental findings and are used in conjunction with static write contours to show how transitions form.