Emerging Materials for Emerging Devices
A. Benfdila, A. Lakhlef and M. Goudjil
Microelectronics and Nanotechnology Research Group, FGEI,
The University M. Mammeri, Tizi-Ouzou, BP 17 RP, DZ15000 Algeria
*Associate ICTP-UNESCO-IAEA, Trieste Italy
The today challenges can be summarized as follows: The increase of Integration density in ULSI Circuits sees an obstacle due to silicon physical and technology limits. Going further in integration needs further investigation in the silicon material such as strained silicon and eventually its substitution by graphene, as well as alternative gate oxides like new Hafnium dioxide. The increase of frequency in high frequency analog systems needs new materials that can lead to higher device performances. Silicon germanium is a candidate for HEMTs or HBTs devices.
Power level switching raising in bipolar, MOS and IGBTs devices, needs switching to silicon carbide. SiC material has a higher power handling capabilities.
Physical and Technology Limits in Silicon Devices
Silicon devices show different limitations according to their utilization and application. Following Moore’s Law, the integration density is getting higher and higher till it is no more possible to raise it with silicon material. Advanced micro-processors are approaching two billions transistors. Silicon dioxide and silicon materials are no more useful. They are gradually substituted by SOI and Strained technology for substrate and advanced hafnium for gate dielectrics. II-V compounds and SiGe are candidates for the next decade. However this substitution will no longer hold in the next decades. Work on graphene and CNTs for different applications is yet started.
In CMOS technology different forms of MOSFETs are investigated and proposed. They rely on drain, oxide and substrate engineering. Drain engineering is basically technology, several geometries have been proposed. Gate engineering in physics and technology aspects have been achieved. New materials such as high k are proposed for the gate oxide and different shapes are investigated for the gate (MUGFETs).
In RF applications many discussions and applications are achieved on HEMT technology and its implementation by HBTs or FETs as shown in Fig.1 for the many Gigaherz transistors. The heterojunction bipolar transistor is seen to be the most suitable for these applications.
In power application, IGBTs are designed using different materials and technology, Vertical engineering and SiC material is used, this allows higher voltage and current sustainability. New IGBTs structures are introduced using alternative materials capable to withstand high voltage and high temperature conditions as shown in Fig. 2
New devices are investigated based on CNTs and Graphene. This may cover a variety of applications (ICs, RF circuits and power devices). In case of CNTs, arrays of transistors are easily achieved. However, scale integration is still not possible; Fig. 3 shows an array of CNTFEs.
Graphene transistors are studied and designed aiming to overcome problems of integration. Experimental studies showed that integration may be achieved provided lot of efforts in materials study and engineering. Typical GrFET is shown in Fig. 4 and the experimental wafer for device integration are under investigation. It is expected that
Fig.1. A HEMT FETs Structure for RF Application Fig. 2 Typical New IGBT Structure
In order to comply with the new applications needs based on new device requirements, emerging materials are to be considered, studied and engineered. Depending on the applications, the materials can be classified as: Materials for advanced ICs, materials for advanced RF circuits and materials for high power devices. For the first application, the candidates for short time are strained silicon, silicon germanium and new hafnium oxides. For long time expectation, Graphene material and corresponding dielectrics are being investigated. Carbon material is being experimented as CNFETs or sensor elements. For the second application, high speed electronics requires materials of very high mobility and higher mobility saturation values. Mainly, Si-Ge is the most promising material besides the new II-V and II-VI materials.
Silicon carbide and other II-VI materials are the key issue for high power application like power MESFETs and IGBTs.
Fig.3. Typical Array of CNFETs Fig.4. Graphene Transistor
For the next decades, materials science and engineering will be the key issue for many device applications. Engineering for emerging materials is among the main topics in future research and development: Graphene will take a higher interest due to its possible successor for ULSI technology. Besides, advanced III-V SC are greatly studied as they will be the media for information transport.