Collaborative Research: nm Electron Wave Devices for Low-Power VLSI Electronics

晶体管是现代集成电路的关键元件。由于一个典型的电路有数十亿个晶体管，晶体管工作时产生的热量限制了芯片的运行速度和晶体管的数量。工业界正在寻求一种晶体管设计，它具有尽可能低的电源电压和关闭时最小的泄漏电流。为了快速切换，它必须在接通时提供大电流。关断电流与通断电流的比率是由一个叫做亚阈值摆幅（SS）的因素决定的；在一个普通的晶体管中，SS被限制为每10年0.06伏，即在开关比中每10:1的因数需要0.06伏的电源电压，而典型的10的8次方开/关比需要8*0.06 v，或约0.5伏。隧道晶体管已被提议降低SS，但这些有小的导通电流，因为电子隧穿的概率，因此有助于电流，是非常小的。没有隧穿晶体管的电子反而被反射。利用电子的波动特性，我们将通过使用额外的反射器来抑制反射，其结构很像抑制来自相机镜头表面的光反射的涂层。如果电子没有被反射，它就会通过晶体管，导通电流就会增加。我们还将开发另一种低ss晶体管，一种超晶格晶体管，它利用电子波特性在晶体管关闭时阻止传输，而在晶体管打开时则不会。该项目的成功将使集成电路功耗降低约5:1，从而使计算机更快、更大、更有用的芯片受益。这是一个关键的更广泛的影响。一个智力上更广泛的影响是基础物理学的使用，电子量子干涉在一个广泛的公共应用设备中。REU和暑期实习是另一个更广泛的影响。该项目旨在用一种新的器件取代VLSI（一个庞大的行业）中的现代晶体管，该器件工作在较低的电压下，具有低开关功率，低断开状态电流，低待机功率和高开启电流，以实现高速。一种提出的晶体管是隧道场效应管，它具有低工作电压和低导通电流，增加了电子波反射器，使反射的电子波产生破坏性干扰。这抑制了电子反射，因此增加了透射，因此增加了通电流。第二个晶体管使用电子源中的超晶格来抑制热电子，从而产生比玻尔兹曼分布更锐利的开关特性。这允许大开：关比在低电压。我们将模拟设计、制造和测试这些晶体管。建模将使用量子输运模拟器（NEMO），并添加散射。制造需要标准的FET制造工艺（在UCSB建立良好），但增加了在MBE通道生长或晶体管MOCVD再生过程中形成的电子能量滤波器。其知识意义是明确的：相干电子效应是大众市场电子器件的基础。

Transistors are the key element in modern integrated circuits (ICs). Since a typical circuit has billions of transistors, heat generated during transistor operation limits how fast the chip can operate and how many transistors it can contain. Industry is seeking a transistor design with the lowest possible power-supply voltage and the smallest amount of leakage current when it is off. To switch quickly, it must provide large currents when it is on. The ratio of off-current to on current is determined by a factor called the sub-threshold swing (SS); in a normal transistor the SS is limited to 0.06 Volts per decade, i.e. each factor of 10:1 in the on-off ratio requires 0.06 Volts power supply voltage, and a typical 10 to the eighth on/off ratio requires 8*0.06V, or about 0.5 Volts. Tunnel transistors have been proposed to reduce the SS, but these have small on-currents because the probability of an electron tunneling, hence contributing to current, is very small. An electron which does not tunnel through the transistor is instead reflected. Exploiting the wave nature of electrons, we will suppress the reflection by using additional reflectors, in a structure much like the coatings which suppress the reflection from light from the surface of a camera lens. If the electron is not reflected, it instead passes through the transistor, and the on-current is increased. We will also develop another low-SS transistor, a superlattice transistor, which exploits electron wave properties to block transmission when the transistor is off but not when it is on. Success in the project would allow a ~5:1 reduction in IC power consumption, leading to faster, bigger, and more useful chips benefitting computers. This is a key broader impact. An intellectual broader impact is the use of fundamental physics, electron quantum interference in a device of vast public application. REU and summer internships are another broader impact. The project seeks to replace the modern transistor in VLSI, a vast industry, with a new device, operating at lower voltage, for low switching power, yet giving low off-state current, for low standby power, and high on current, for high speed. One proposed transistor is a tunnel-FET, which has low operating voltage but low on-current, with added electron wave reflectors which cause destructive interference of the reflected electron wave. This suppresses electron reflection, hence increases transmission, hence on-current. The second transistor uses a superlattice in the electron source to suppress hot electrons, thereby producing on:off characteristics sharper than a Boltzmann distribution. This allows large on:off ration at low voltages. We will model (simulate) design, build and test these transistors. Modelling will use quantum transport simulators (NEMO) with the addition of scattering. Fabrication requires standard FET fabrication processes (well established at UCSB), but adds electron energy filters formed either during MBE channel growth or during MOCVD regrowth of the transistors. The intellectual significance is clear: coherent electron effects as the basis of a mass-market electron device.