Design and characterization of a 3D encapsulation with silicon vias for radio frequency micro-electromechanical system resonator

In this paper, we present a three-dimensional（3D） vacuum packaging technique at a wafer level for a radio frequency micro-electromechanical system（RF MEMS） resonator, in which low-loss silicon vias is used to transmit RF signals.Au–Sn solder bonding is adopted to provide a vacuum encapsulation as well as electrical conductions. A RF model of the encapsulation cap is established to evaluate the parasitic effect of the packaging, which provides an effective design solution of 3D RF MEMS encapsulation. With the proposed packaging structure, the signal-to-background ratio（SBR） of 24 dB is achieved, as well as the quality factor（Q-factor） of the resonator increases from 8000 to 10400 after packaging.The packaged resonator has a linear frequency–temperature（ f –T） characteristic in a temperature range between 0℃ and 100℃. And the package shows favorable long-term stability of the Q-factor over 200 days, which indicates that the package has excellent hermeticity. Furthermore, the average shear strength is measured to be 43.58 MPa among 10 samples.

Effects of polarization on intersubband transitions of Al_xGa_(1-x)N/GaN multi-quantum wells

The effects of polarization and related structural parameters on the intersubband transitions of A1GaN/GaN multi- quantum wells （MQWs） have been investigated by solving the Schr6dinger and the Poisson equations self-consistently. The results show that the intersubband absorption coefficient increases with increasing polarization while the transition wavelength decreases, which is not identical to the case of the interband transitions. Moreover, it suggests that the well width has a greater effect on the intersubband transitions than the barrier thickness, and the intersubband transition wavelength of the structure when doped in the barrier is shorter than that when doped in the well. It is found that the influences of the structural parameters differ for different electron subbands. The mechanisms responsible for these effects have been investigated in detail.

Enhanced photoluminescence and stability of ZnSe microspheres/Cs4PbBr6 microcrystals/CsPbBr3 nanocrystals composites

A ternary complex combining dual-phase perovskites-Cs4PbBr6/CsPbBr3(DP-CPB) with ZnSe micropshere s(ZnSe-DP-CPB) was succes s fully prepared using supersaturated recrystallization technique at room temperature.It was showed that the DP-CPB composites were partially embedded in ZnSe microsphere composed with ZnSe NCs.The light absorption range of ZnSe-DP-CPB composites was extended from visible to near infrared light.Highly enhanced luminescence from ZnSe-DP-CPB composite was observed and the excitation power-dependent photoluminescence showed that the recombination involves excitons.The recombination lifetimes of the ternary composites increased compared with DP-CPB composite,indicating that the non-radiative combination was suppressed which maybe possibly due to the decrease of both bulk and surface defects,owing to the passivation of ZnSe,as well as the suitable band alignments of these three components.The ternary complex also showed improved stability of photoluminescence(PL),which opens a newavenue for enhancing the stability of PL and optoelectronic applications for semiconductor-perovskite composites.

Reliability testing of a 3D encapsulated VHF MEMS resonator

The frequency stability of a three-dimensional（3D） vacuum encapsulated very high frequency（VHF）disk resonator is systematically investigated. For eliminating the parasitic effect caused by the parasitic capacitance of the printed circuit board（PCB）, a negating capacitive compensation method was developed. The testing results implemented at 25 ℃ for 240 h for the long-term stability indicates that the resonant frequency variation remained within ±1 ppm and the noise floor derived from Allan Deviation was 26 ppb, which is competitive with the conventional quartz resonators. The resonant frequency fluctuation of 1.5 ppm was obtained during 200 temperature cycling between -40 and 85 ℃.

Photonic bandgap structure and long-range periodicity of a cumulative Fibonacci lattice

In this work, we study the photonic band of cumulative Fibonacci lattices, of which the structure is composed of all generated units in a Fibonacci sequence. The results are compared with distributed Bragg reflector(DBR)structures with the same numbers of layers. Photonic bandgaps are found at two characteristic frequencies, symmetrically separated from the central bandgap in the DBR counterpart. Field amplitude and phase distribution in the Fibonacci lattice indicates an interferential origin of the bandgaps. Fourier transform on the refractive index profile is carried out, and the result confirms a determinate long-range periodicity that agrees well with the photonic band structure.

Pristine PN junction toward atomic layer devices

In semiconductor manufacturing,PN junction is formed by introducing dopants to activate neighboring electron and hole conductance.To avoid structural distortion and failure,it generally requires the foreign dopants localize in the designated micro-areas.This,however,is challenging due to an inevitable interdiffusion process.Here we report a brand-new junction architecture,called"layer PN junction",that might break through such limit and help redefine the semiconductor device architecture.Different from all existing semiconductors,we find that a variety of van der Waals materials are doping themselves from n-to p-type conductance with an increasing/decreasing layer-number.It means the capability of constructing homogeneous PN junctions in monolayers'dimension/precision,with record high rectification-ratio(>10^(5))and low cut-off current(<1 pA).More importantly,it spawns intriguing functionalities,like gate-switchable-rectification and noise-signal decoupled avalanching.Findings disclosed here might open up a path to develop novel nanodevice applications,where the geometrical size becomes the only critical factor in tuning charge-carrier distribution and thus functionality.

A low-jitter RF PLL frequency synthesizer with high-speed mixed-signal down-scaling circuits

A low-jitter RF phase locked loop（PLL） frequency synthesizer with high-speed mixed-signal down-scaling circuits is proposed.Several techniques are proposed to reduce the design complexity and improve the performance of the mixed-signal down-scaling circuit in the PLL.An improved D-latch is proposed to increase the speed and the driving capability of the DMP in the down-scaling circuit.Through integrating the D-latch with ＇OR＇ logic for dual-modulus operation,the delays associated with both the ＇OR＇ and D-flip-flop（DFF） operations are reduced,and the complexity of the circuit is also decreased.The programmable frequency divider of the down-scaling circuit is realized in a new method based on deep submicron CMOS technology standard cells and a more accurate wire-load model.The charge pump in the PLL is also realized with a novel architecture to improve the current matching characteristic so as to reduce the jitter of the system.The proposed RF PLL frequency synthesizer is realized with a TSMC 0.18-μm CMOS process. The measured phase noise of the PLL frequency synthesizer output at 100 kHz offset from the center frequency is only -101.52 dBc/Hz.The circuit exhibits a low RMS jitter of 3.3 ps.The power consumption of the PLL frequency synthesizer is also as low as 36 mW at a 1.8 V power supply.

CMOS ring VCO for UHF RFID readers

A complementary metal oxide semiconductor （CMOS） voltage controlled ring oscillator for ultra high frequency （UHF） radio frequency identification （RFID） readers has been realized and characterized. Fabricated in charter 0.35 p.m CMOS process, the total chip size is 0.47 × 0.67 mm^2. While excluding the pads, the core area is only 0.15 ×0.2 mm^2. At a supply voltage of 3.3 V, the measured power consumption is 66 mW including the output buffer for 50 Ω testing load. This proposed voltage-controlled ring oscillator exhibits a low phase noise of - 116 dBc/Hz at 10 MHz offset from the center frequency of 922.5 MHz and a lower tuning gain through the use of coarse/fine frequency control.

Layer-number dependent high-frequency vibration modes in few-layer transition metal dichalcogenides induced by interlayer couplings

Two-dimensional transition metal dichalcogenides（TMDs） have attracted extensive attention due to their many novel properties.The atoms within each layer in two-dimensional TMDs are joined together by covalent bonds,while van der Waals interactions combine the layers together.This makes its lattice dynamics layer-number dependent.The evolutions of ultralow frequency（〈 50 cm^（-1）） modes,such as shear and layer-breathing modes have been well-established.Here,we review the layer-number dependent high-frequency（〉 50 cm^（-1）） vibration modes in few-layer TMDs and demonstrate how the interlayer coupling leads to the splitting of high-frequency vibration modes,known as Davydov splitting.Such Davydov splitting can be well described by a van der Waals model,which directly links the splitting with the interlayer coupling.Our review expands the understanding on the effect of interlayer coupling on the high-frequency vibration modes in TMDs and other two-dimensional materials.

A 130 nm CMOS low-power SAR ADC for wide-band communication systems

This paper presents a low power 9-bit 80 MS/s SAR ADC with comparator-sharing technique in 130 nm CMOS process. Compared to the conventional SAR ADC, the sampling phase is removed to reach the full efficiency of the comparator. Thus the conversion rate increases by about 20% and its sampling time is relaxed. The design does not use any static components to achieve a widely scalable conversion rate with a constant FOM. The floorplan of the capacitor network is custom-designed to suppress the gain mismatch between the two DACs. The ＇set-and- down＇ switching procedure and a novel binary-search error compensation scheme are utilized to further speed up the SA bit-cycling operation. A very fast logic controller is proposed with a delay time of only 90 ps. At 1.2 V supply and 80 MS/s the ADC achieves an SNDR of 51.4 dB and consumes 1.86 mW, resulting in an FOM of 76.6 fJ/conversion-step. The ADC core occupies an active area of only 0.089 mm2.