This paper presents a novel method for controller design for a dual input single output (DISO) system with application to a robot for printing layouts at construction sites. The differential drive robot has a separately controlled linear actuator that moves the print head perpendicularly to the fore-aft axis of the robot. The output is the lateral position of the print head; the sum of the position of the linear actuator (faster stage) relative to a reference point on the front of the robot, which is determined by the steering of the robot (slower stage). Both are measurable. The controller coordinates the action of the separately controlled linear actuator and the differential steering to achieve fast convergence and sub-millimeter tracking. Simulations and experimental results demonstrate the effectiveness of the approach.

Major strides in on-chip power conversion have been made by IBM in case of their POWER8TM processor (1), and by Intel in case of their 4th generation (Haswell) processor (2), although neither company’s new on-chip voltage regulator (VR) uses an integrated inductor. After outlining why on-chip power conversion is so desirable, this talk will highlight the important role of magnetic inductors in power conversion, and will review recent developments in, and prospects for, magnetic materials for inductors, especially those formed by plating methods. Granular DC-DC power delivery, consisting of fast dynamic voltage scaling for each load through use of a dedicated VR, can significantly improve energy efficiency. Traditionally, the large size of the inductor component has impeded efforts to fabricate the VR in one module. The preferred approach to shrinking the inductor is to increase the switching frequency. The downside to higher frequency operation is reduced efficiency and increased heat dissipation. Thus, shrinking the inductor involves a compromise of space vs. performance, and placing the VRM with an integrated inductor on the processor using thin-film fabrication processes is a natural, if challenging, progression. In thin-film ferromagnetic inductors, yoke material and thicknesses (typically 1 - 3 microns) can be tailored to reach desired inductance values (e.g., 10 – 40 nH), while endeavoring to maintain high enough operating frequency (e.g., 50 – 100 MHz). Considerable efforts have gone into developing new magnetic alloys with higher resistivity (> 100 µΩcm) to reduce yoke eddy currents. A notable example produced by sputtering is amorphous Co91.5Zr4Ta4.5 (CZT) [3, 4], which seems to have become the standard against which other materials are compared. This has been used as the yoke material in inductors fabricated on top of 90 nm CMOS structures by Gardner et al. [5], for example. Electroplating has been a standard technique for the deposition of thick metal films due to its high deposition rate, conformal coverage and low cost. It was an enabling technology for the thin-film magnetic recording head, and was thus used for yoke fabrication for our inductors (6, 7). For the latter, Ni45Fe55 was chosen over Ni80Fe20 for its higher magnetic moment (1.6T), high anisotropy field, and higher electrical resistivity (40 µΩcm). Plated Co-based materials are attractive alternatives to Ni-Fe as yoke materials, e.g. due to their higher moment, especially if their resistivity can be made to approach or exceed 100 µΩcm. We are exploring the use of electrolessly-plated, Co-W-P films for inductor applications (8). The electroless Co-W-P films show excellent magnetic properties, with good magnetic anisotropy, and coercivity of less than 0.1 Oe (Fig. 1). The resistivity of the films is about 90-100 µΩcm, which is close to that of most amorphous Co-based alloys. [1] Z. Toprak-Deniz et al., ISSCC Digest, 112 (2014). [2] E. A. Burton, et al., Proc. Applied Power Electronics and Expositions (IEEE-APEC), p. 432-439 (2014) [3] K. Hayashi et al., J. Appl. Phys., 61, 2983 (1987). [4] D. S. Gardner et al., IEEE Trans. Magn. 43, 2615 (2007). [5] D. S. Gardner et al., J. Appl. Phys., 103, 07E927 (2008). [6] N. Wang et al., J. Appl. Phys., 111, 07E732 (2012). [7] N. Sturcken et al., ISSCC, 48, 244 (2013). [8] N. Wang et al., MMM-Intermag, paper HG-11, 2013 Fig. 1. Hysteresis loop (left) and SEM Xsection (right) of an electrolessly-plated Co-W-P films. This work was supported in part by Lawrence Livermore National Laboratory subcontract No. B601996 under prime contract DE-AC52-07NA27344 from the U.S. Government. Inductor fabrication was carried out in the Microelectronics Research Laboratory (MRL) at IBM’s T. J. Watson Research Center.

Air-core slab inductors with specially designed current return paths are proposed to achieve the ultra-high Q required for on-chip power delivery and management at >90% efficiency. Uniquely optimized for buck converter circuits, this CMOS-compatible structure avoids the challenges of thin-film magnetics. Q~25-30 at 200-300MHz is experimentally demonstrated.

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.

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.

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 described, including high frequency permeability measurements. The inductance of 2-turn coil inductors, for example, was enhanced up to about 6 times over the air core equivalent, with an inductance density of 130 nH/mm2 being achieved. The resistance of these non-laminated inductors was relatively large at high frequency due to magnetic and eddy current losses but is expected to improve as the yoke material/structure is further optimized, making electroplated yoke-containing inductors attractive for dc-dc power converters.