| As a new electronic device using the spin of electron,spintronic devices can store and calculate information by regulating the spin properties of electrons,and have excellent characteristics such as ultra-high speed,nonvolatile and anti irradiation.At present,spintronic devices are regarded as potential candidates to replace traditional CMOS devices.Through electrical,thermal,magnetic,optical and other manipulation methods,the device can obtain super-high switching speed and ultra-low static power consumption.It is hopeful to overcome the problem of physical limit in traditional CMOS devices and revolutionize the semiconductor technology.At present,the developed spintronic devices include magnetic random access memory,spin transfer moment nano-oscillator,spin logic device and so on.With the arrival of the era of big data,the digital system needs to receive and process a large amount of information through analog-to-digital converter(ADC)at the same time,which drives ADC to obtain higher sampling rate and lower power consumption.However,with the CMOS process feature sizes scaling down,the problems of aperture jitter,static power consumption and stability of the sample-and-hold circuit restrict the performance improvement of ADC.Rencently,more researches focusing on the regulation of spin have emerged,and some researchers have proposed some spin-based ADC designs.Compared with the traditional ADC,it has some significant advantages as followed:(1)It provides a new solution to the difficulty of high performance ADC design caused by the decrease of CMOS feature size.(2)Exploiting the intrinsic property of spin,super-high speed,ultra-low power consumption and non-volatile analogto-digital conversion can be realized.(3)Based on the architecture of spintronic devices,computing in memory can be obtained,which is expected to promote the implementation of non-von Neumann architecture.This theis focuses on the application of novel ADC design,presenting a new type of spin ADC based on magnetic tunnel junction.The function realization,structure optimization and performance parameters of the designed device are analyzed and researched.The main innovations are as follows:1.A dual-bit spin comparator based on magnetic tunnel junctions is proposed utilizing spin Hall effect and spin orbit torque,a dual-bit spin comparator is presented which is composed of two identical MTJs and a layer of heavy metal(HM)thin films.Besides,based on this dual-bit structure,a double-check estimation algorithm is presented to improve the reliability of the device.The viriation of magnetic moment in the device is analyzed by establishing a macrospin model.The bit error rate caused by temperature is calculated numerically,and the Dzyaloshinskii-Moriya interaction in the multilayer film is researched by micromagnetic simulation.The simulation results show that the two MTJs in the comparator can be switched simultaneously due to spin Hall effect with nanosecond switching time,which is higher in working speed and lower in static power consumption compared with the traditional CMOS comparator.The proposed double-check estimation algorithm also significantly enhances the robustness of the device and reduces the bit error rate in switching the MTJ caused by thermal noise and other interference.Compared with the comparator based on a single MTJ,the accuracy of the dual-bit comparator can be improved by up to 24%.At the same time,the influence of DMI on the magnetic moment state has been explored,and the material optimization scheme of the device is proposed.Not only achieving the goal of improving the performance of devices,but also providing a new idea for improving the reliability of spintronic devices based on MTJs.2.A dual-bit spin ADC is proposedBased on the proposed dual-bit spin comparator,a dual-bit Flash-like spin ADC is presented.By setting the MTJ arrays at the top and bottom of the HM layer,a 3-bit Flash ADC composed of eight dual-bit spin comparators is formed.Different from the traditional Flash ADC,which obtains multiple reference thresholds through partial resistance strings.By changing the shape of heavy metal layers to obtain linear reference thresholds at different comparators,the proposed structure can quantify the input signal as the magnetic moment states of the MTJ arrays.The working process of the device is simulated and modeled,and the calculation results show that the proposed dual-bit spin ADC has nanosecond conversion speed.The highest sampling rate can reach 667 MHz,and the power consumption is only 0.17 p J.Also,the reliability of our design is better than previous spin ADCs.In addition,in order to improve the thermal stability of the device and reduce the difficulty of device fabrication and circuit complexity,a differential spin ADC is presented based on the promotion of the structure above.The design can generate a set of opposite digital codes at the same time,and the sampling rate of spin ADC can be further improved by using self-reference reading method. |
