加热器顶置间接加热GeTe相变的四端口高速射频开关

High-speed four-port indirect-heating phase-change switch with a top microheater based on GeTe

针对传统加热器中置间接加热相变开关的固有切换速度缓慢难题,本文提出一种加热器顶置的射频开关新结构,即加热器顶置的间接加热相变材料四端口开关(four-port indirect heating phase change switch with a top microheater,FIPCS-T),通过热传导过程自上而下的定向性,建立了更加有效的焦耳热能量利用方法.新结构中不同射频参数的仿真表明,FIPCS-T结构对升温过程和淬火过程均能有效缩短相变材料达到临界温度的时间,升温过程比淬火过程的缩短更加显著.相比于传统中置间接加热相变开关,FIPCS-T的升温-淬火环节时间缩短20%以上,这不仅显著提高了切换速度,同时还降低了相变材料的重结晶风险,结合相变材料本身具有的高频低损耗特征及其器件结构设计的灵活性,从而可在微波、毫米波、太赫兹等超大范围频段内提供反射小、插损低和端口隔离度高的高速射频开关.尽管人们对GeTe相变材料在信息存储等方面的应用开展了多年研究,但其特殊相变特征能否解决未来射频开关面临的高性能需求,仍然存在诸多挑战.本文研究结果表明,GeTe热相变机理与PIN二极管、微机电系统(microelectromechanical systems,MEMS)等其他原理相比,新射频开关的速度更快、工作频率更高、插入损耗更低.在射频开关特性验证的基础上,我们构建了由5个FIPCS-T单元组成的缺陷地结构(defected ground structure,DGS)可重构滤波器,实现了滤波器频率和带宽的重构,证明了开关状态组合对滤波器媒质特性的调控能力;再通过5个单元FIPCS-T开关状态的组合与电致热控制,实现了低通、带通滤波特征的可重构,为未来大规模天线、大规模电路等先进可重构无线电系统的智慧调控提供了全新的射频开关机理和方法.同时,引入类似相变存储器多值方案的控制方法,可有效提升相变开关的调控和选择维度,增加可调控的性能范围和参数,实现其他类型开关不能实现的更深层次调控优势.

Radio-frequency(RF)switches are widely used in integrated multifunctional systems and multiple/massive antenna wireless systems for on-demand RF circuit/channel processing,such as transmitter/receiver conversion,band selection,parameter adjustment/adaptation,phase delay,beam forming/beam scanning,and network reconfiguration in wireless communication systems or radars.Following the changing trends from a single antenna to antenna arrays,microwave to millimeter/terahertz bands,and several circuits/channels to circuit/channel stacks,traditional switching technologies based on PIN diodes,complementary metal-oxide-semiconductor(CMOS),microelectromechanical systems(MEMS),and other technologies are encountering bottlenecks in terms of bandwidth and insertion loss.Recently,phase-change materials(PCMs),such as VO2 and Ge Te,have attracted considerable attention as new switching technologies,which provides a novel idea for the control of antenna arrays and RF circuit stacks.As a new material for future switches,the low resistivity of PCMs in a crystal state ensures low resistance when connected to RF circuits,which is the key to achieving low insertion loss of the switch.Usually,a PCM switch needs one or more microheaters to heat the PCM with direct or indirect-heating type,whether in a two-or four-port switch.In the directheating phase-change switch,the direct-connection method requires additional matching networks,which increases the design difficulty and overall complexity.Therefore,the indirect-heating structure has currently become the main direction.In the indirect-heating type,the RF-signal path is usually separated from the heating path using high and low thermal conductivity materials.To overcome the previous limitations of the direct heating with heavy cross-interference and indirect heating with low switching speed,the present study introduces a fast-response Ge Te material for a proposed new indirect-heating RF-switch structure with a top microheater that simplifies the manufacturing process,reduces device structural complexity,and widens operating-frequency range.The structure is composed of a four-port indirect-heating PCM switch with a top microheater(FIPCS-T),which guides the heat flow in a top-to-down mode,thus enabling a more efficient utilization method of the Joule-heat energy.The simulation results show that the FIPCS-T can shorten the transition time of PCMs to reach critical temperature in both the heating and quenching processes.Shortening of the heating process is more significant than that of the quenching process.The entire heating-quenching process takes 68.11 ns,which is 20%shorter than the traditional indirect-heating phase-change switch with a central microheater.This process not only improves the switching speed of indirect-heating phase-change switches but also effectively reduces the risk of PCM recrystallization.In addition,the results show that FIPCS-T demonstrates low reflection,low insertion loss,and high port-isolation performance from microwave to the millimeter/terahertz band.Although Ge Te PCMs have been investigated for many years as future fast input/output storage media,their potentiality to satisfy future RF switch challenges has not been previously studied.The current study reveals this obscurity.Compared with PIN diodes and MEMS,RF switches based on Ge Te provide several advantages,e.g.,highspeed switching,high-frequency operation,low insertion losses,and easy integration with various circuits.Furthermore,according to the proposed Ge Te RF switch,a defected ground structure(DGS)reconfigurable filter with five FIPCS-Ts is designed,which is applied to verify the electronic-to-heating dynamic reconfiguration in the operating frequency and bandwidth.According to the combination of five FIPCS-Ts on/off switching,low-pass and band-pass filter types with different bandwidths are realized in the frequency range of 0–10 GHz.In summary,in addition to its general advantages,FIPCS-T,as a new structure of indirect-heating RF switches,provides the following two important features.It offers a fast state transition for high-speed switching using the top-to-down heatflow-control method with better heat efficiency,and it provides a very small volume for potential integrated application by changing the relative position between the microheater and Ge Te material layer to simplify the device structure.In addition,the DGS reconfigurable filter illustrates that the on-demand electromagnetic characteristics of a device with multiple FIPCS-T and Ge Te material layers are feasible by controlling each FIPCS-T state in the FIPCS-T array in a massive antenna and giant circuit stack systems.The adjustable and controllable characteristics can satisfy many important future requirements,such as fast beam forming,beam scanning,RF circuit switching,channel multiparameter dynamic adaptation,and multifunctional RF devices for future wireless communication and radar.