Design and Fabrication of Bond Wire Micro-Magnetics

This thesis presents a new approach for the design and fabrication of bond wire magnetics for power converter applications by using standard IC gold bonding wires and micro-machined magnetic cores. It shows a systematic design and characterization study for bond wire transformers with toroidal and race-track cores for both PCB and silicon substrates. Measurement results show that the use of ferrite cores increases the secondary self-inductance up to 315 µH with a Q-factor up to 24.5 at 100 kHz. Measurement results on LTCC core report an enhancement of the secondary self-inductance up to 23 µH with a Q-factor up to 10.5 at 1.4 MHz. A resonant DC-DC converter is designed in 0.32 µm BCD6s technology at STMicroelectronics with a depletion nmosfet and a bond wire micro-transformer for EH applications. Measures report that the circuit begins to oscillate from a TEG voltage of 280 mV while starts to convert from an input down to 330 mV to a rectified output of 0.8 V at an input of 400 mV. Bond wire magnetics is a cost-effective approach that enables a flexible design of inductors and transformers with high inductance and high turns ratio. Additionally, it supports the development of magnetics on top of the IC active circuitry for package and wafer level integrations, thus enabling the design of high density power components. This makes possible the evolution of PwrSiP and PwrSoC with reliable highly efficient magnetics

A 32 mV/69 mV input voltage booster based on a piezoelectric transformer for energy harvesting applications

This paper presents a novel method for battery-less circuit start-up from ultra-low voltage energy harvesting sources. The approach proposes for the first time the use of a Piezoelectric Transformer (PT) as the key component of a step-up oscillator. The proposed oscillator circuit is first modelled from a theoretical point of view and then validated experimentally with a commercial PT. The minimum achieved start-up voltage is about 69 mV, with no need for any external magnetic component. Hence, the presented system is compatible with the typical output voltages of thermoelectric generators (TEGs). Oscillation is achieved through a positive feedback coupling the PT with an inverter stage made up of JFETs. All the used components are in perspective compatible with microelectronic and MEMS technologies. In addition, in case the use of a ∼40 μH inductor is acceptable, the minimum start-up voltage becomes as low as about 32 mV

Design of low-voltage integrated step-up oscillators with microtransformers for energy harvesting applications

This paper describes the modeling of startup circuits in battery-less micropower energy harvesting systems and investigates the use of bond wire micromagnetics. The analysis focuses on step-up Meissner oscillators based on magnetic core transformers operating with input voltages down to ≈100 mV, e.g. from thermoelectric generators. As a key point, this paper examines the effect of core losses and leakage inductances on the startup requirements obtained with the classical Barkhausen criterion, and demonstrates the minimum transconductance for oscillations to occur. For validation purposes, a step-up oscillator IC is fabricated in a STMicroelectronics 0.32 μm technology, and connected to two bond-wire microtransformers, respectively, with a 1:38 MnZn ferrite core and with a 1:52 ferromagnetic low-temperature co-fired ceramic (LTCC) core. Coherently with the proposed model, experimental measurements show a minimum startup voltage of 228 mV for the MnZn ferrite core and of 104 mV for the LTCC core

Smart energy management and conversion

This chapter introduced power management circuits and energy storage unit designs for sub‐1 mW low power energy harvesting technologies, including indoor light energy harvesting, thermoelectric energy harvesting and vibration energy harvesting. The solutions address several of the problems associated with energy harvesting, power management and storage issues including low voltage operation, self‐start, efficiency (conversion efficiency as well as impact of power consumption of the power management circuit itself), energy density and leakage current levels. Additionally, efforts to miniaturize and integrate magnetic parts as well as integrate discrete circuits onto silicon are outlined to offer improvements in cost, size and efficiency. Finally initial results from efforts to improve energy density of storage devices using nanomaterials are introduced

Design Optimization of Integrated Magnetic Core Inductors

This paper presents a design study of novel geometrical configurations for miniaturized toroidal planar core thin-film inductors. A standard core with square-shaped toroidal geometry is compared to a new core with serpentine toroidal geometry. The mathematical model of the inductor demonstrates the possibility to further increase the maximum inductance value for closed or air-gap core inductors in a given footprint area (up to +35% in 16 mm2), by means of a more efficient use of the core surface area in case of serpentine geometry, assuming the same coupling factor for both windings. Furthermore, the presented serpentine geometry increases performances in terms of magnetic energy density and quality factor while retaining higher inductance values, at the cost of a limited increase of layout complexity. This paper provides also a more accurate estimation of the inductance of a square shaped toroidal inductor based on the evaluation of the mean magnetic path length accounting for the non-uniformity of the magnetic flux density in the core cross section and for the corner effect

Process for the measurement of the hardness and for the selection of agricultural products

Method for measuring the hardness of agricultural products comprising the operations of: - implementing a test program suitable for identifying and selecting one or more indices (S3, S4) which can be measured with a non-destructive test on a respective product/fruit, correlated with the hardness (Du) of the same product/fruit, measured by a respective penetration test; - calculating the coefficients that define the straight line representative of the linear correlation between said indices and the hardness for the respective product. The method is implemented with the operations of: - applying on the product a dynamic force, preferably of impulsive type; - detecting the mechanical reaction through at least a piezoelectric transducer capable of generating an electric signal based on the application or transmission of said dynamic force through the respective kiwi fruit; - analyzing said electric signal relative to the fruit, and measuring the crossing time of said dynamic force through the same kiwi fruit; - calculating the value of the index S4 of said dynamic force through the fruit. It was found that the S4 index has a very significant correlation with the hardness of the respective kiwi fruit, and that the coefficients of the relative correlation straight line are respectively a = -1.5084, and b = 0.0072

Design and Optimization Techniques of Over-Chip Bondwire MicroTransformers with LTCC core

This paper describes the realization of bond-wire micro-magnetics by using standard bonding-wires and a toroidal ferromagnetic LTCC core with high resistivity. The proposed fabrication procedure is suitable for the development of magnetic components on top of an IC with small profile and small size (< 15 mm2). A transformer is designed and applied over-chip, working in the MHz range with high inductance (~33 \u3bc H) and high effective turns-ratio (~20). Applications include bootstrap circuits and micro-power conversion for energy harvesting. Measurements demonstrate a maximum secondary Q-factor of 11.6 at 1.3 MHz, and a coupling coefficient of 0.65 with an effective turns ratio of 19, which are among the highest values reported for toroidal miniaturized magnetics. The achieved inductance density is 2 \u3bcH/mm2, along with an inductance per unit core volume of 15.6 \u3bcH/mm3, and a DC inductance-to-resistance ratio of 2.23 \u3bcH/\u3a9. The presented technique allows to obtain over-chip magnetics trough a post-processing of the core, and it is also suitable for highdensity power supply in package (PwrSiP) and power supply on chip (PwrSoC). Finally, a series of optimization techniques for planar core magnetic devices in order to maximize the inductance per unit area are discussed and applied to the considered case