T.L. Ren

Synthesis of Cu-modified Co2Z hexaferrite with planar structure by a citrate precursor method

Abstract Co2Z hexaferrite is a planar anisotropic iron oxide which can present high values of permeability at high frequency. In this paper, Cu-modified Co2Z hexaferrites powders were synthesized at a low temperature using a citrate precursor method. The formation of Z-type phases was characterized by X-ray diffraction and magnetization measurements. It is found that phase formation temperature and sintering temperature were influenced directly by the content of copper. The effects of Cu-substitution on the microstructure and high frequency properties of the ceramics have been investigated.

On-chip soft-ferrite-integrated inductors for RF IC

Systematic investigation of novel CMOS-compatible on-chip ferrite-integrated RF inductors is reported. New ferrite-fully-filled solenoid inductor is achieved, using low-temperature ferrite nano-powder-mixed-photoresist inkjetting/spin-coating technique we developed, which shows significant improvement of +160% in L and +220% in Q, to multi-GHz. An improved equivalent circuit for new ferrite-integrated inductors is developed. This work shows excellent prospects for making compact high-quality on-chip soft-ferrite-integrated inductors for RF SoCs.

Fully integrated ferrite-based inductors for RF ICs

Ferrite thin-film RF integrated inductors using IC compatible processes are proposed firstly. Ferrites (Co-based, CoFe-based, MnZn-based, NiZn-based and garnet) for RF integrated inductors are investigated, and CoZrO shows the suitable high-frequency performance for RF applications. Various inductors with different kinds of ferrite thin-films have been fabricated using fully integrated processes. A typical inductor sample with CoZrO thin-film is presented. The L and Q values of the sample are 2.05 nH and 20.5 at 2 GHz, respectively. The inductance is raised by 17% and the quality factor is raised by 41%, compared with the inductor which does not include a ferrite thin-film. With the improvement of L and Q, the size of ferrite thin-film inductors can be reduced significantly.

Stacked-spiral RF inductors with vertical nano-particle-magnetic-medium

A new concept of stacked-spiral inductor with vertical near-closed-circuit nano-particle-magnetic-core in CMOS is reported. Prototypes, fabricated in a 6-Al-metal CMOS backend process using ferrite nano-particles, show a high inductance-density of 825nH/mm2 in multi-GHz, which is promising for making super compact inductors in RF SoC.

Dependence of GMR on NiFe layer thickness in high sensitive simple spin valve

The dependence of the giant magnetoresistance on Ni/sub 81/Fe/sub 19/ soft magnetic layer thickness is investigated experimentally for a simple spin valve with a top-pinned structure of Ta (6 nm)/Ni/sub 81/Fe/sub 19//Co/sub 90/Fe/sub 10/ (1 nm)/Cu (1.8 nm)/Co/sub 90/Fe/sub 10/ (3.5 nm)/Ir/sub 20/Mn/sub 80/ (8 nm)/Ta (6 nm). With Ni/sub 81/Fe/sub 19/ thickness increased from 6 nm to 7 nm, the magnetoresistance (MR) ratio decreases sharply from 8.34% to 3.34%, whereas it changes only slightly within the thickness ranges from 2-6 nm and from 7-12 nm, and larger MR ratios are obtained in the range from 2-6 nm. For a spin valve with an optimized thickness of Ir/sub 20/Mn/sub 80/ (11 nm) and top Ta (3 nm), the MR dependence is in accordance with the former structure when Ni/sub 81/Fe/sub 19/ thickness changes from 3.5 to 5.5 nm, and an optimized spin valve with 4.5-nm-thick Ni/sub 81/Fe/sub 19/ is obtained. This spin valve has a large MR ratio (9.15%), low coercive force (0.85 Oe), and high sensitivity, which makes it promising for applications.

Microstructure and properties of nanosructured strontium lead titanate ceramic

Abstract Nanostructured ceramics of strontium lead titanate (Pb0.5Sr0.5TiO3) were obtained by fast-sintering at 1150°C ∽1200°C from nanosize powder prepared by stearic acid gel method. The microstructure was characterized by means of X-ray diffraction, scanning electronic microscopy, transmission electronic microscopy, atom force microscopy and phase detection microscopy. The size effect on structure as well as ferroelectric property was investigated. The phase transition of nanostructured strontium lead titanate ceramic was found to be correlated with a diffused phase transition. The transition temperature shifs to low temperature with decreasing grain size.

Thin film thermal conductivity metrology using photoluminescence of quantum dots

Studying thin film thermal conduction is important in the development of many heat related sensors, actuators and microsystems. Emerging non-contact metrologies of membrane thermal conductivity show several advantages when devices are scaling down or novel materials are utilized. In this paper, a method to evaluate membrane thermal conductivity is presented using quantum dots as temperature markers. As an example, the thermal conductivity of 290nm-thick crystalline silicon thin film is measured as 106±10W/(m·K). Compared to conventional methods, the features of this method, like fine spatial resolution and non-contact temperature probe, bring the measurement robustness against ambient disturbance and the reduction on measurement system error. Furthermore, this metrology is eligible for thin films of other materials.

Nano-powder-magnetic-core vertically stacked-spiral RF inductor in CMOS

This paper reports a novel concept of vertically stacked-spiral RF inductor with integrated nano-powder-magnetic-core in standard CMOS. Prototype inductors in a foundry 0.18µm 6-metal CMOS and a post-CMOS backend process module (i.e., CMOS+) are fabricated and measured. Result shows the proof-of-concept designs greatly increase the inductance, L, by up to 34% and the factor, Q, by 62% over a multi-GHz frequency range.