Hanqiao Zhang

Tailoring High-Frequency Properties of Permalloy Films by Submicrometer Patterning

We have measured shape-induced high frequency properties of patterned submicrometer permalloy (Py) arrays. We sputtered and patterned Py films on gold (Au) transmission lines, using chromium (Cr) as adhesion layers for Au and Py deposition. Each Py bar in the arrays is 10 mum long and 100 nm thick. The widths of the Py bars in two different arrays are 240 and 550 nm, respectively. Micromagnetic simulations indicate single domain magnetization distribution in these Py structures. The measured ferromagnetic resonance frequencies without bias field are approximately 11.5 and 8 GHz, respectively. We obtained the corresponding susceptibilities. The experimental results agree with theoretical predictions.

Direct Current Effects on High-Frequency Properties of Patterned Permalloy Thin Films

We have investigated experimentally direct current (dc) effects on high-frequency properties of two different permalloy (Py) submicrometer patterns of 0.24 mum and 0.55 mum width, 10 mum length, and 100 nm thickness. The natural ferromagnetic resonance (FMR) frequencies for the two samples are about 8.5 and 11.5 GHz. A 50 mA dc produces a FMR frequency reduction of about 1 GHz in both samples. We extracted susceptibility spectra for the samples from the measurement data. We studied inductance variations of Py embedded transmission lines for different dc levels. With 50 mA dc, the operational frequencies of the inductances decreased by 9% and 12.5%. We also tested effects of magnetic fields generated by external magnets on the submicrometer patterns for comparison. To obtain the same magnetization rotation angle, the external magnetic field needs to be about five times larger than the Ampere field created by the direct current. This behavior is unique and may be associated with the increased thermal energy from the Joule heating effects.

Direct-current effects on magnetization reversal properties of submicron-size Permalloy patterns for radio-frequency devices

Ferromagnetic resonance (FMR) spectroscopy is used to measure direct-current (dc) effects on the magnetization reversal properties of submicron-sized lateral patterned magnetic material. The observed FMR frequency-field relationship shows that for both 240 and 550 nm wide Permalloy (Py) nanowires the coercivity is reduced by ∼33% when a 50 mA dc passes through the transmission line where the nanowires are incorporated. The temperature dependence of the coercivity has a T relationship which suggests the coherent rotation mode tendency in such 100 nm thick Py nanowires.Ferromagnetic resonance (FMR) spectroscopy is used to measure direct-current (dc) effects on the magnetization reversal properties of submicron-sized lateral patterned magnetic material. The observed FMR frequency-field relationship shows that for both 240 and 550 nm wide Permalloy (Py) nanowires the coercivity is reduced by ∼33% when a 50 mA dc passes through the transmission line where the nanowires are incorporated. The temperature dependence of the coercivity has a T relationship which suggests the coherent rotation mode tendency in such 100 nm thick Py nanowires.

Thermoelectric performance of NiyMo3Sb7−xTex(y≤0.1, 1.5≤x≤1.7)

Mo3Sb7−xTex is a high temperature thermoelectric material, reported to reach figure of merit (ZT)=0.8 at 1023 K. Various p-type samples of NiyMo3Sb7−xTex were prepared with y≤0.1 and 1.5≤x≤1.7 via high temperature reactions at 993 K. Adding transition metal atoms into the empty cube formed by Sb atoms significantly alters the band structure and thus the thermoelectric properties. Electronic band structure calculations indicate that adding Ni slightly increases the charge carrier concentration, while higher Te content causes a decrease. Thermoelectric properties were determined on pellets densified via hot pressing at 993 K. Seebeck as well as electrical and thermal conductivity measurements were performed up to 1023 K. The highest ZT value thus far was obtained from a sample of nominal composition Ni0.06Mo3Sb5.4Te1.6, which amounts to 0.93 at 1023 K.

High performance tunable slow wave elements enabled with nano-patterned permalloy thin film for compact radio frequency applications

Slow wave elements are promising structures to design compact RF (radio frequency) and mmwave components. This paper reports a comparative study on different types of coplanar wave-guide (CPW) slow wave structures (SWS). New techniques including the use of defected ground structure and the different signal conductor shape have been implemented to achieve higher slow wave effect with comparative loss. Results show that over 42% and 35% reduction in length is reported in the expense of only 0.3 dB and 0.1 dB insertion loss, respectively, which can end up with 66% and 58% area reduction for the design of a branch line coupler. Implementation of the sub micrometer patterned Permalloy (Py) thin film on top of the simple SWS has been demonstrated for the first time to increase the slow wave effect. Comparing with the traditional slow wave structure, with 100 nm thick Py patterns, the inductance per unit length of the SWS has been increased from 879 nH/m to 963 nH/m. The slow wave effect of the designed structur...

A new method for high-frequency characterization of patterned ferromagnetic thin films

A new high-frequency method is presented for patterned ferromagnetic thin film characterization. Parasitic effects, which often overwhelm the signal from patterned ferromagnetic structures, are significantly reduced through an on-chip interference process. As a result, measurement sensitivity is greatly improved in comparison with conventional on-chip transmission line ferromagnetic resonance (FMR) methods. Algorithms are given to extract the complex permeability and FMR linewidth of ferromagnetic materials from scattering parameters obtained with the method. An on-chip 10 GHz structure was fabricated and experimentally demonstrated ∼20 dB parasitic effect cancellation efficiency. A patterned Permalloy (Py) array with 180 stripes is measured. Each stripe is 100 nm thick, 2 μm wide, and 20 μm long. The FMR frequency of the patterned Py thin films was tuned with an external static magnetic field. With a 676 G bias field, the obtained FMR frequency and linewidth are 9.68 and 1.4 GHz, respectively. These resu...

Direct current tunable noise suppressor using sub-micrometer patterned permalloy films

A tunable noise suppressor at gigahertz frequency using sub-micrometer patterned Permalloy (Py) loaded coplanar waveguide transmission line is presented. The transmission line consists of 100 nm thick Py patterns on top of 0.9 μm thick gold lines. Measured results show that the stop band frequency of the noise suppressor is changed from 4.8 GHz to 6 GHz depending on the aspect ratios of Py patterns. Variation of the gap in between Py patterns changed the stop band frequency from 4 GHz to 6 GHz. Furthermore, a novel way of tuning the stop band frequency of the noise suppressor by using an external direct current is reported. By applying 150 mA direct current along the transmission line, the frequency is changed from 6 GHz to 4.3 GHz. The measured results of 1.5% pass band loss, 2° transmitted signal phase distortion, and 3 dB extra return loss of the designed noise suppressor are demonstrated. Noise suppression frequency and the magnitude of signal attenuation can be further improved by increasing the thic...

Broadband Mag-Noise of Patterned Permalloy Thin Films

A Y-factor noise figure (NF) measurement method is developed to characterize high-frequency mag-noise of a 550 nm wide Permalloy strip array under different dc bias currents. The noise voltage density is obtained. The proposed lumped element transmission line model describes noise properties of the patterned Py array well. Measurement data show that rapid ferromagnetic resonance frequencies (FMR) shift induced by dc bias current is related to the excess magnetization fluctuation thermally created by the combined dc current Joule heating effects and orthogonal Oersted fields.

Characterisation and modelling of mitered coplanar waveguide bends on silicon substrate

Mitered coplanar waveguide (CPW) bends are cascaded to form meandered CPW lines. Test samples are fabricated and characterised. In this article a compact, CAD-oriented semi-empirical equivalent circuit model is presented. The validity of the model is verified by comparing it with the experimental and simulation results. It is demonstrated that a meandered CPW with mitered bends has higher characteristic impedance and lesser loss when compared to straight CPWs.

High-Frequency Properties of Permalloy Nanowire Arrays for RF Devices

We present our simulation and experimental results on high-frequency properties of permalloy (Py) nanowire arrays. The planar Py nanowires are 10 mum long, 100 nm thick with widths of ~ 240 nm, and ~ 500 nm (layout dimension). The distance between adjacent Py nanowires is ~ 100 nm. OOMMF simulations indicate that single domain structures exist in these nanowires with ferromagnetic resonance frequencies (FMR) around 10 GHz. Coupling effects are negligible. The Oersted field of an external DC current reduces the FMR frequencies. The obtained Py properties can be used to simulate RF inductors to evaluate the application potentials of Py nanowire arrays in RF devices.