The School of Electronic Engineering at Peking University invented the Van Hoff cold source transistor.
As integrated circuits continue to evolve towards advanced nodes, reducing power consumption has become one of the core challenges facing information processing systems in the post-Moore's Law era. The subthreshold swing (SS) of traditional silicon-based metal-oxide-semiconductor transistors (MOSFETs) is limited by the Boltzmann distribution, making it difficult to exceed 60mV/dec at room temperature. This physical limit prevents further reduction in the operating voltage Vdd, and power consumption tends to become a bottleneck as device size shrinks.
Recently, a research team led by Assistant Researcher Jia Si and Professor Zhiyong Zhang from the Carbon-Based Electronics Research Center and the Key Laboratory of Nanodevice Physics and Chemistry of the Ministry of Education, School of Electronic Engineering, Peking University, proposed and experimentally verified a van Hove cold source transistor (VHS FET). This device utilizes the characteristic of quasi-one-dimensional semiconductors where the density of states drops sharply near the van Hove singularity. The Fermi level in the source region can be precisely tuned to a specific van Hove singularity through electrochemical doping or electric field manipulation to construct a "cold source" (Figure 1). This approach, which uses the same quasi-one-dimensional semiconductor material for both the source and channel to form a homojunction, allows for direct injection of cold carriers, reduces interface scattering, simplifies the device structure, and facilitates miniaturization.
The research team chose semiconductor-type carbon nanotubes to construct the van Hough source and channel (Figure 2). In this device, the main gate is responsible for switching control, while the auxiliary control gate precisely modulates the Fermi level in the source region. When the Fermi level approaches the van Hough singularity of the carbon nanotube, the source state density decreases sharply with energy, effectively filtering high-energy carriers and forming a steep hot-emission switch (Figure 3). Experimental results show that the VHS FET based on a single carbon nanotube achieves a subthreshold swing of 49 mV/dec at room temperature, significantly breaking the Boltzmann limit. At a gate length of 450 nm and an operating voltage of 0.5 V, the normalized on-state current of this device is comparable to that of a 22 nm node silicon-based transistor, while the operating voltage is 0.25 V lower than that of the silicon-based device (Figure 4). This result demonstrates that van Hough sources can not only achieve steep switching characteristics below 60 mV/dec but also maintain high current drive capability, providing design ideas for the development of a new generation of ultra-low-power steep-slope transistors.
