Takayuki Sakai

Thin Film Deposition by Low Energy SiCln+ Beam

The reaction between mass-separated low-energy (30 eV) SiCln+ ion beams and Si and SiO2 substrates was studied to investigate the influence of the number of Cl atoms in SiCln species on their deposition characteristics. It has been found that the deposition yield of Si is positive (deposition) at n=1 and it becomes negative (etching) at n=3 on the Si substrate while it is nearly zero on SiO2. In the presence of O2 gas, the deposited species change to silicon oxides and the deposition of SiO2 also takes place on SiO2 with SiCl3+. The etching of Si by SiCl3+, however, takes place and the etching yield was found to be unaffected by O2. These results can be explained if adsorbed Cl atoms are assumed to desorb as SiCl2, leaving either Si or Cl on the substrate depending on the value of n. In the O2 ambience, the preferred bonding of Si with O leads to the deposition of SiO2, except in the case of SiCl3+ on Si where excess Cl atoms react with Si.

Plasma Parameters in Low-Pressure Ar-Hg Discharge Plasma Used for Liquid Crystal Display Back-Lighting.

The electron temperature and electron density in the tube axis of a low-pressure Ar–Hg discharge lamp with 4 mm bore diameter have been measured under various bath temperatures with a probe method. Results show that the relative changes in the bath temperature dependence of electron temperature and electron density are similar to those obtained in the 36 mm I.D. discharge tubes. However, the electron temperature values are twice as large. The electron densities measured by the four methods used here are in good agreement with one another, indicating the reliability of the results.

Bounded Depth Circuits with Weighted Symmetric Gates: Satisfiability, Lower Bounds and Compression

A Boolean function f:{0,1}^n -> {0,1} is weighted symmetric if there exist a function g: Z -> {0,1} and integers w_0, w_1, ..., w_n such that f(x_1, ...,x_n) = g(w_0+sum_{i=1}^n w_i x_i) holds. In this paper, we present algorithms for the circuit satisfiability problem of bounded depth circuits with AND, OR, NOT gates and a limited number of weighted symmetric gates. Our algorithms run in time super-polynomially faster than 2^n even when the number of gates is super-polynomial and the maximum weight of symmetric gates is nearly exponential. With an additional trick, we give an algorithm for the maximum satisfiability problem that runs in time poly(n^t)*2^{n-n^{1/O(t)}} for instances with n variables, O(n^t) clauses and arbitrary weights. To the best of our knowledge, this is the first moderately exponential time algorithm even for Max 2SAT instances with arbitrary weights. Through the analysis of our algorithms, we obtain average-case lower bounds and compression algorithms for such circuits and worst-case lower bounds for majority votes of such circuits, where all the lower bounds are against the generalized Andreev function. Our average-case lower bounds might be of independent interest in the sense that previous ones for similar circuits with arbitrary symmetric gates rely on communication complexity lower bounds while ours are based on the restriction method.

Improved Exact Algorithms for Mildly Sparse Instances of Max SAT

We present improved exponential time exact algorithms for Max SAT. Our algorithms run in time of the form O(2^{(1-mu(c))n}) for instances with n variables and m=cn clauses. In this setting, there are three incomparable currently best algorithms: a deterministic exponential space algorithm with mu(c)=1/O(c * log(c)) due to Dantsin and Wolpert [SAT 2006], a randomized polynomial space algorithm with mu(c)=1/O(c * log^3(c)) and a deterministic polynomial space algorithm with mu(c)=1/O(c^2 * log^2(c)) due to Sakai, Seto and Tamaki [Theory Comput. Syst., 2015]. Our first result is a deterministic polynomial space algorithm with mu(c)=1/O(c * log(c)) that achieves the previous best time complexity without exponential space or randomization. Furthermore, this algorithm can handle instances with exponentially large weights and hard constraints. The previous algorithms and our deterministic polynomial space algorithm run super-polynomially faster than 2^n only if m=O(n^2). Our second results are deterministic exponential space algorithms for Max SAT with mu(c)=1/O((c * log(c))^{2/3}) and for Max 3-SAT with mu(c)=1/O(c^{1/2}) that run super-polynomially faster than 2^n when m=o(n^{5/2}/log^{5/2}(n)) and m=o(n^3/log^2(n)) respectively.

Solving Sparse Instances of Max SAT via Width Reduction and Greedy Restriction

We present a moderately exponential time polynomial space algorithm for sparse instances of Max SAT. Our algorithms run in time of the form O(2(1 − μ(c))n ) for instances with n variables and cn clauses. Our deterministic and randomized algorithm achieve \(\mu(c) = \Omega(\frac{1}{c^2\log^2 c})\) and \(\mu(c) = \Omega(\frac{1}{c \log^3 c})\) respectively. Previously, an exponential space deterministic algorithm with \(\mu(c) = \Omega(\frac{1}{c\log c})\) was shown by Dantsin and Wolpert [SAT 2006] and a polynomial space deterministic algorithm with \(\mu(c) = \Omega(\frac{1}{2^{O(c)}})\) was shown by Kulikov and Kutzkov [CSR 2007].

High Responsivity in an Optically Controlled Field-Effect Transistor Using the Direct Wafer Bonding Technique

An optically controlled field-effect transistor (FET) in which the GaAs FET region and the GaInAs/InP light absorption region were directly bonded is demonstrated. This device offers high optical- to-electrical conversion efficiency. In this work, we report the electrical and optical characteristics of this device based on the direct wafer bonding technique. The bonding temperature dependence on the device characteristics and responsivity characteristics were also measured. As a result, we achieved a high responsivity of more than 150 A/W.

Bonding temperature dependence of optically controlled field-effect transistor fabricated by direct wafer bonding technique

An optically controlled field-effect transistor (FET) in which the GaAs FET region and the GaInAs/InP light absorption region were directly bonded was demonstrated. The temperature dependence of the direct bonding and its effect on the performance of the optically controlled FET were examined. A maximum current modulation rate of 60% and a responsivity of more than 150(A/W) were obtained.

Improved exact algorithms for mildly sparse instances of Max SAT

Abstract We present improved exponential time exact algorithms for Max SAT. Our algorithms run in time of the form O ( 2 ( 1 − μ ( c ) ) n ) for instances with n variables and m = c n clauses. In this setting, there are three incomparable currently best algorithms: a deterministic exponential space algorithm with μ ( c ) = 1 O ( c log ⁡ c ) due to Dantsin and Wolpert (2006) [9] , a randomized polynomial space algorithm with μ ( c ) = 1 O ( c log 3 ⁡ c ) and a deterministic polynomial space algorithm with μ ( c ) = 1 O ( c 2 log 2 ⁡ c ) due to Sakai, Seto and Tamaki (2015) [30] . Our first result is a deterministic polynomial space algorithm with μ ( c ) = 1 O ( c log ⁡ c ) that achieves the previous best time complexity without exponential space or randomization. Furthermore, this algorithm can handle instances with exponentially large weights and hard constraints. The previous algorithms and our deterministic polynomial space algorithm run super-polynomially faster than 2 n only if m = O ( n 2 ) . Our second results are deterministic exponential space algorithms for Max SAT with μ ( c ) = 1 O ( ( c log ⁡ c ) 2 / 3 ) and for Max 3-SAT with μ ( c ) = 1 O ( c 1 / 2 ) that run super-polynomially faster than 2 n when m = o ( n 5 / 2 / log 5 / 2 ⁡ n ) and m = o ( n 3 / log 2 ⁡ n ) respectively. Our third result is a randomized exponential space algorithm for Max SAT with μ ( c ) = 1 O ( c 1 / 2 log 3 / 2 ⁡ c ) that run super-polynomially faster than 2 n when m = o ( n 3 / log 5 ⁡ n ) .