|Title:||Chiral anomaly-based transistors for low-dissipation computing|
|Advisors:||Chai, Yang (AP)|
Electronic circuit design
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Applied Physics|
|Pages:||xxix, 108 pages : color illustrations|
|Abstract:||As charge-based electronics are reaching their physical limits in reducing power consumption, the devices based on new physics mechanisms with low-dissipation transport characteristics offer opportunities to improve energy efficiency. In this thesis, we design and demonstrate three types of field-effect transistors based on chiral anomaly current in topological materials, including (1) Modulation of the chiral anomaly to achieve field-effect electronics with Dirac semimetal. (2) Topological transistors with Weyl semiconductor. (3) Room-temperature valley-based electrochemical transistor with high ON/OFF ratio Firstly, we demonstrate field-effect chiral anomaly devices with Dirac semimetal PtSe2. In analogous to valley degree of freedom in semiconductor, chiral anomaly current in Weyl/Dirac semimetals is theoretically predicted to be low loss over a long distance but still lacks experimental ways to efficiently control its transport. Here, we demonstrate field-effect chiral anomaly devices with Dirac semimetal PtSe2, in which the Dirac point is close to the Fermi level. Through electrostatic gating with ionic liquid, we can modulate the chiral anomaly conductance by the external field with an ON/OFF ratio of more than 103 and realize basic logic functions in the device by regarding electric and magnetic fields as input signals. The chiral anomaly is further corroborated with nonlocal valley transport measurement, which can also be effectively modulated through magnetic and electrical fields, showing robust nonlocal valley transport with the diffusion length at the micrometre scale. Our works provide a way to manipulate chiral anomaly current for low-power electronics.|
Secondly, we demonstrate the topological transistors with the Weyl semiconductor. The field-effect transistors with topological semiconductors can show low-dissipation transport based on the chiral anomaly in the "ON" state and topologically trivial "OFF" state, which promises low-power electronics. Here we demonstrate topological FETs with a high ON/OFF ratio by modulating the energy separation between Fermi level and Weyl point of Weyl semiconductor Te. By electrostatic manipulation of EF, there is topological phase change between Weyl semimetal and semiconductor, and the negative magnetic resistance induced by chiral anomaly current reaches up to -90% in the Weyl semimetal state. We have achieved both enhancement and depletion mode FETs, with ~108 ON/OFF ratio under ≤2 V gating, 5.74×106 ON/OFF by -1 V gating and ultrahigh low-dissipation ON conductance of 100 mS, superior to the performance of general charge-based FETs and much higher than reported spin/valley FETs (about 101-103 ON/OFF). Furthermore, we have demonstrated multiple terminal and angle-switching logic functions in a single device, which is high area efficiency. Our results provide new strategies for preparing high ON/OFF FETs, which is promising for supplementing conventional charge-based electronics. Thirdly, we have successfully achieved a valley-based electrochemical transistor with a high ON/OFF ratio at room temperature. As a quantum degree of freedom of electrons, the valley exhibits low-dissipation transport characteristics for carrying information with high energy efficiency. However, it still remains a grand challenge to efficiently operate the valley transistor at room temperature and realize basic digital and analogue computing functions. Here we demonstrate valley transistors with more than 7 μm diffusion length based on Weyl semiconductor (Te) at room temperature. The electrical double layer can volatilely shift EF and modulate valley transistor with an ON/OFF ratio of 105. The ion intercalation/extraction can cause a non-volatile shift of EF, showing 32 linear, symmetrical and discrete non-volatile states with low cycle-to-cycle variation (0.37%) for neuromorphic computing with the accuracy of 95.2% for classifying handwriting data. The coexistence of ion adsorption and intercalation mechanism results in the dynamic ion response with the high nonlinearity (4.35) and short-term memory curve for reservoir computing. The accuracy for temporal signal reaches as high as 95%. Our studies show the potential of low-power valley transistors for computing at room temperature. In conclusion, we investigate the chiral anomaly-based transistors, which show the potentials of overcoming the physical limits (unavoidable heat dissipation) of the charge-based electronics. Modern electronics demands high performance with extreme energy efficiency (e.g., abundant data computing). Our device shows potentials to address this issue: high ON/OFF ratio transfer curve, basic logic functions (AND, OR) and room-temperature neuromorphic computing to deal with static and dynamic information.
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