Semiconductor breakthrough: intelligent calcium ion implantation


According to Look Around You, an investigative scientific program appearing on the BBC’s Channel 3, a new atomic element that may revolutionize semiconductor fabrication has been successfully formulated in laboratory conditions. This element is Intelligent Calcium (see above) which may replace sodium ion implantation in the near future and thereby increase both digital and analog circuit performance.


From a design standpoint, ion implantation is one of the crucial steps in integrated circuit manufacturing as it allow the designer some freedom to set the threshold voltage for a MOSFET transistor as well as negate some of the potential problems with manufacturing. The basic idea is that by applying a positive or negative voltage at the gate terminal, we can attract either negative or positive charges (pairs of which are constantly thermally generated) to the “top” of the device respectively. If enough of these charges accumulate, we can form a conducting channel through the substrate. By implanting immobile ions in the gate oxide region, we can change the voltage at which this channel formation begins to occur and thereby the required bias for transistor operation. It is not hard to imagine that some chemical process steps may add undesired ions at the silicon-oxide interfaces in addition to dangling bonds in the oxide, so this same technique may sometimes be used to balance the parasitic ion concentration due to processing and return the device to the designed activation threshold.

Typically, the positive ion of choice is sodium. Ions are generated by electrically heated metal and are then accelerated by electromagnetic fields until the impact the target. Upon impacting the crystal lattice, the sodium looses momentum and typically does not move from its resting position unless the device is severely heated (can happen!). The sodium’s only action is to interact with the charges around it and modulate the effective threshold voltage for the device. The main downside is that the sodium ion cannot ‘decide’ when to act, so its effects are constant throughout time.

This is where the concept of intelligent calcium comes in. Unlike the ‘dumb’ sodium, the intelligent calcium’s higher atomic weight allows it higher flexibility with its charge configuration and thereby more freedom to ‘decide’ when to act as a 2+ valence ion and when to pretend to be neutrally charged. By using intelligent calcium as a positive ion throughout an integrated circuit, a calcium network is formed where each atom becomes a node and can communicate with both adjacent and far-away atoms to get a general feel for the situation and the activity of the device. It can then modulate its charge to increase (or decrease) the individual transistor thresholds as needed. From an analog perspective, the transconductance of the device goes up tremendously as well as the frequency response (due to intelligent calcium’s rapid activation). From a digital perspective, the speed of information propagation in the intelligent calcium network exceeds the mobilities of both holes and electrons, even in a strained silicon lattice. For this reason, the transistors adjust their threshold in advance of the gate voltage changes and thereby increase their switching speeds. This in turn translates to quicker gates and overall quicker devices.

The future is bright for intelligent calcium as it has many desirable properties for semiconductor fabrication. Scientists are presently pushing the bleeding edge of technology as they investigate the possibility of using the intelligent calcium network as a means to communication between transistors and a total replacement for the metal interconnects. The progress is slow, however, I have full confidence that I will one day have the opportunity to image an metal-less, intelligent calcium powered device in the weekly IC Friday column.