Inevitably, as with most reviews, the focus of this article will be on the things I think could be improved upon rather than what is perfect. In this case, the latter would be a very tedious review because there is so much about this review that I like. The former, however, will be a matter of opinion and there will surely be disagreements about what, if anything, could be changed.

Nanomaterials For Transistors And Memory Cells

This was an area in which the new paper made a substantial difference and I think it will be of great interest to the community. I will discuss the material aspects of the work and then move on to the implications for future research.

Graphene Transistor Foils

In the previous year, we saw an explosion of research papers published on graphene and related two-dimensional nanomaterials. The reason for this is clear – functionalization of these materials has led to a large increase in the number of properties that can be harnessed. One such example is the transistor – a three-terminal device in which current can be controlled by a voltage applied to a gate electrode. The new paper takes the form of a mini-review by Zhang and co-workers and is entitled “Graphene Transistor Foils”. This paper examines the use of graphene and other two-dimensional nanomaterials in transistors and, in particular, the role that these materials play in the manufacture of flexible transistors. 

The paper begins by discussing the progress that has been made in developing flexible graphene transistors. One of the earliest approaches involved using a transfer technique to transfer monolayer graphene onto a plastic substrate. While this demonstrated the potential for graphene in flexible electronics, it was not an altogether easy process and inevitably, some of the graphene was damaged during the transfer process. This technique was then improved upon using a “graphene foil”, which is essentially a chemically etched graphene film. The authors of this paper performed a survey of the different flexible graphene transistors that have been developed and found that while some worked well, most were plagued by low yields and high defect density. In addition to this, most of the graphene transistors that were examined were based on a Schottky architecture, which is built upon metal-semiconductor contacts and is thus, not highly compatible with CMOS technology.

Graphene-Based Memory Cell Schemes

One of the interesting features of the paper by Zhang et al. is the variety of schemes that they have developed to utilize graphene and other two-dimensional nanomaterials as the basis for novel types of non-volatile memory cell. These schemes range from the use of intercalated metals and organic molecules to the formation of polymer-based memory cells. To begin with, let us discuss the use of graphene and other two-dimensional nanomaterials in the manufacture of ferroelectric field-effect transistors (FeFETs) – the devices that will be discussed in more detail below. These FETs are inherently non-volatile because the ferroelectric switching of the material used to build them (PZT, BaTiO3 or even HfO2) protects the data stored in them. Hence, they retain their data even when the power supply is switched off. 

In a flexible FeFET, the graphene is not glued to a rigid substrate, but is, instead, deposited upon a poly(ethylene terephthalate) (PET) film. This provides the flexibility that is required for the manufacture of flexible devices. The paper by Zhang et al. also discusses other methods of forming flexible non-volatile memory cells based on the use of graphene.

Graphene-Derived Heterostructure For High-Performance NAND Flash Memories

Next, I will discuss two papers by S.W. Pattinson and coauthors, which form part of a special issue of ACS Nano on “Graphene-Based Nanomaterials”. These papers investigate the use of graphene and related nanomaterials in the fabrication of high-performance non-volatile memory cells. The first of these, “A Graphene-Derived Heterostructure For High-Performance NAND Flash Memories”, is a mini-review by Pattinson and co-workers published in the Journal of American Chemical Society. In this paper, the authors examine the structure-performance relationship in graphene-based memories and determine that there is a direct correlation between the two. This is an important relationship to establish because it means that the structure of the memory cell determines the functional performance of the device (in this case, the device is a non-volatile NOR flash memory cell).

To begin with, the authors examine in detail the role of the substrate in the performance of the cell and how different types of substrates can affect the behavior of the device. This is important because, as the authors demonstrate, the charge carrier mobility in graphene is high and, as a result, this material can be used to create high-performance cells. However, this depends upon the choice of the substrate used and the authors examine various types of substrates, including silicon, copper, glass and plastic. In each case, the authors examine how the charge carrier mobility in the graphene layer changes and, in turn, how this affects the functional performance of the device. For example, if we compare silicon and glass as the substrate, we find that carrier mobility drops by a factor of two in the case of silicon and an order of magnitude in the case of glass. This has important ramifications for the design of high-performance memory cells, especially those based upon graphene.

Graphene Semiconductors For Low-Voltage Operation

Now, I will turn to the work performed by Ji and co-workers, which is entitled “Graphene Semiconductors For Low-Voltage Operation” and published in the journal ACS Nano. This is a mini-review by Ji and co-workers, which examines the effect of substrate choice on the “on/off” voltage of the transistor. For low-voltage operation, it is desirable for the transistor to operate at the lowest possible voltage (to minimize power consumption) and these materials provide just such an opportunity. In particular, the authors of this paper examine the effect that different substrates (such as silicon, sapphire and glass) have on the “on/off” voltage of the transistor. Interestingly, the authors found that while all three of these substrates have a negative effect upon the “on/off” voltage, sapphire had the least negative effect. This makes it a viable option for low-voltage transistor building blocks.

The Impact Of Graphene In Today’s Technology

Ultimately, this mini-review article cannot discuss the role of graphene in technology without mentioning the significant progress that has been made in the area of flexible electronics. Specifically, I will focus on the technology behind the Kodak wearable photo printing film and the fact that this is one of the first functional products that makes use of graphene.

As I discussed above, graphene is an extremely versatile material and forms the basis of many promising technologies. The above papers indicate that graphene-based devices have many advantages, including high thermal conductivity, high radiation tolerance and low processing temperatures. These are all significant advantages for future technology and the papers discussed here demonstrate that graphene is well-positioned to take a significant role in many areas, including flexible electronics.