Multidot single-electron devices (SEDs) can enable new types of computing technologies, such as those that are reconfigurable and reservoir-computing. A self-assembled metal nanodot array film that is attached to multiple gates is a candidate for use in such SEDs for achieving high functionality. However, the single-electron properties of such a film have not yet been investigated in conjunction with optimally controlled multiple gates because of the structural complexity of incorporating many nanodots. In this study, Fe nanodot-array-based double-gate SEDs were fabricated by vacuum deposition, and their single-electron properties (modulated by the top- and bottom-gate voltages; VT and VB, respectively) were investigated. The phase of the Coulomb blockade oscillation systematically shifted with VT, indicating that the charge state of the single dot was controlled by both the gate voltages despite the metallic random multidot structure. This result demonstrates that the Coulomb blockade oscillation (originating from the dot in the multidot array) can be modulated by the two gates. The top and bottom gates affected the electronic state of the dot unevenly owing to the geometrical effect caused by the following: (1) vertically asymmetric dot shape and (2) variation of the dot size (including the surrounding dots). This is a characteristic feature of a nanodot array that uses self-assembled metal dots; for example, prepared by vacuum deposition. Such variations derived from a randomly distributed nanodot array will be useful in enhancing the functionality of multidot devices.
An o p t i m i z a t i o n of advanced s e l f -a l i g n e d t r a n s i s t o r s f o r a low-power ECL c i r c u i t has been s t u d i e d . The ECL c i r c u i t h a s been f a b r i c a t e d with t h e 0.5-pm r u l e and a 30-GHz fT technology and has been e v a l u a t e d i n terms of t h e p r o p a g a t i o n d e l a y t i m e of r i n g o s c i l l a t o r s and a 1 / 8 s t a t i c d i v i d e r . W e have obtained 39-ps/1.6-mW ECL c i r c u i t and 12.5-GHz 1 / 8 s t a t i c d i v i d e r . I n t r o d u c t i o n B i p o l a r ECL LSIs a r e t h e components i n h i g h p e r f o r m a n c e d i g i t a l s y s t e m s s u c h a s m a i n f r a m e c o m p u t e r s a n d b r o a d b a n d t r a n s m i s s i o n systems. Today, ECL performance i s sub-100 p s i n 10K-gate V L S I s ( 1 ) . However, t h e demand f o r h i g h e r s p e e d and l a r g e r i n t e g r a t i o n i s i n c r e a s i n g , while t h e power d i s s i p a t i o n has not changed much because of t h e c o o l i n g problem. I n t h i s work, we have s t u d i e d t h e o p t i m i z a t i o n Analysis of ECL c i r c u i t The p r o p a g a t i o n d e l a y t i m e of an ECL c i r c u i t can be expressed a s t h e summation of t h e v a r i o u s CR t i m e c o n s t a n t s . A t o F : Ccb : Cbe : Csub: CL : r e : RL : P r o p o r t i o n a l i t y c o n s t a n t s Collector-base junction capacitance Base-emitter junction capacitance Cje + d i f f u s i o n capacitance Cdk C o l l e c t o r -s u b s t r a t e junction capacitance P a r a s i t i c capacitance of pull-up r e s i s t o r and i n t e r c o n n e c t i o n Base r e s i s t a n c e (sum of i n t e r n a l and e x t e r n a l ) Emitter s e r i e s r e s i s t a n c e Re + d i f f e r e n t i a l r e s i s t a n c e kT/qIc Pull-up r e s i s t o r value of ECL c i r c u i t The propagation d e l a y time of a low-power ECL c i r c u i t made by t h e conventional ESPER process has been analyzed with S P I C E c i r c u i t s i m u l a t o r b a s e d on e q u a t i o n 1 t o f i n d which t i m e c o n s t a n t p l a y s t h e most s i g n i f i c a n t r o l e i n determining t h e delay time ( F i g . 1 ) . The power CH2771-4/89/0000(0169)$1 .OO @ 1989 IEEE T -1 d i s s i p a t i o n of t h e ECL g a t e was s e t t o 1 . 6 mW. I t i s found t h a t 4 1 % of t h e d e l a y time i s due t o t h e t i m e c o n s t a n t Ccb(RL+re) and 28% t o C b e r e . T o improve t h e d e l a y t i m e , i t i s e f f e c t i v e t o r e d u c e t h e s e t i m e c o n s t a n t s . Among t h e s e parameters, RL and r e a r e of f i x e d v a l u e s determined by t h e switching c u r r e n t of t h e I n forward b i a s c o n d i t i o n , Cdk r a t h e r than Cje i s a dominant f a c t o r . T h e r e f o r e , s m a l l e r dimensions and h i g h e r c u t -o f f frequency ( f T ) must be r e a l i z e d t o o b t a i n lower Ccb and Cbe. Process designCcb has been reduced by minimizing t h e base r e g i o n with t h e 0.5-pm d e s i g n r u l e . The t r a n s i...
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