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Single-atom transistor could revolutionize electronics

Feb. 19, 2012
Courtesy of the University of New South Wales
and World Science staff

Phys­i­cists say they’ve paved the way for fu­ture leaps in com­put­ing pow­er by mak­ing a tran­sis­tor so small that its cen­tral com­pon­ent is one at­om. But more work re­mains be­fore the full ben­e­fits of this can be reaped, they cau­tion.

Tran­sis­tors are ti­ny de­vices, used in most mod­ern elec­tron­ics, that en­a­ble com­put­ers to per­form log­ic opera­t­ions. The lit­tle gad­gets can ei­ther am­pli­fy a small cur­rent or switch a cur­rent on and off. The “on-off” ca­pa­bil­ity cre­ates the 0’s and 1’s that form com­put­er code. The in­ven­tion of tran­sis­tors in the mid-20th cen­tu­ry, and their sub­se­quent grad­u­al shrink­age, is largely what has en­a­bled com­put­ers to con­stantly get smaller and more pow­erful.

Now, phys­i­cists at the Uni­vers­ity of New South Wales in Aus­tral­ia have cre­at­ed a work­ing tran­sis­tor con­sist­ing of a sin­gle at­om placed pre­cisely in a sil­i­con crys­tal. The de­vice, de­scribed to­day in a pa­per pub­lished in the jour­nal Na­ture Nan­o­tech­nol­ogy, uses a phos­pho­rus at­om po­si­tioned be­tween oth­er mi­nus­cule com­po­nents, known as elec­trodes and con­trol gates.

In the past, sin­gle-at­om tran­sis­tors have been formed more or less by chance in lab­o­r­a­to­ries, but “this is the first time an­y­one has shown con­trol of a sin­gle at­om in a sub­strate with this lev­el of pre­cise ac­cu­ra­cy,” said re­search­er Michelle Sim­mons, who led the proj­ect. How­ev­er, she cau­tioned, sev­er­al hur­dles will need to be over­come be­fore the de­vice can en­ter eve­ry­day use.

The team used an in­stru­ment called a scan­ning tun­nel­ling mi­cro­scope, which can both “see” and ma­ni­pu­late at­omic-scale ob­jects, to move around at­oms at the sur­face of the crys­tal in a vac­u­um. Sev­er­al ad­di­tion­al steps were re­quired be­fore fi­nal­ly, the struc­ture was en­cap­su­lat­ed with a sil­i­con lay­er and the de­vice con­tacted elec­tric­ally. Its elec­tron­ic prop­er­ties matched the­o­ret­i­cal pre­dic­tions for a de­vice of its type, re­search­ers said.

Pre­dic­tions have es­ti­mat­ed that tran­sis­tors will reach the sin­gle-at­om lev­el by about 2020 to keep pa­ce with “Moore’s Law,” an on­go­ing trend in com­put­er hard­ware that sees the num­ber of chip com­po­nents dou­ble eve­ry 18 months. The new ad­vance has de­vel­oped the tech­nol­o­gy to make this pos­si­ble well ahead of sched­ule and gives val­u­a­ble in­sights to ma­n­u­fac­tur­ers in­to how de­vices will be­have once they reach the at­omic lim­it, Sim­mons said.


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Physicists say they’ve paved the way for future leaps in computing power by shrinking a transistor—the key component of computer logic circuits—to a size of just one atom. But more work remains before the full benefits of this can be reaped, they caution. Transistors are tiny devices, used in most modern electronics, that enable computers to perform logic operations. The little gadgets can either amplify a small current or switch a current on and off. The “on-off” capability creates the 0’s and 1’s that form computer code. The invention of transistors in the mid-20th century, and their subsequent gradual shrinkage, is largely what has enabled computers to constantly get smaller and more powerful. Now, physicists at the University of New South Wales in Australia have created a working transistor consisting of a single atom placed precisely in a silicon crystal. The device, described today in a paper published in the journal Nature Nanotechnology, uses a phosphorus atom positioned between other minuscule components, known as electrodes and control gates. In the past, single-atom transistors have been formed more or less by chance in laboratories, but “this is the first time anyone has shown control of a single atom in a substrate with this level of precise accuracy,” said researcher Michelle Simmons, who led the project. However, she cautioned, several hurdles will need to be overcome before the device can enter everyday use. The team used an instrument called a scanning tunnelling microscope, which can both “see” and manipulate atomic-scale objects, to move around atoms at the surface of the crystal in a vacuum. Several additional steps were required before the finally, the structure was encapsulated with a silicon layer and the device contacted electrically. Its electronic properties matched theoretical predictions for a device of its type, researchers said. Predictions have estimated that transistors will reach the single-atom level by about 2020 to keep pace with “Moore’s Law,” an ongoing trend in computer hardware that sees the number of chip components double every 18 months. The new advance has developed the technology to make this possible well ahead of schedule and gives valuable insights to manufacturers into how devices will behave once they reach the atomic limit, Simmons said.