A study of x-ray damage effects on the short channel behavior of IGFET’s

Ionizing particles and radiation may play an important, albeit undesirable role in the processing of VLSI and ULSI circuits in that they can generate bulk charge in the gate insulator of IGFETs. In this regard, there is conflicting information in the literature on the effects of ionizing radiation on short channel phenomena in IGFETs. For example, Peckeraret al. in 1983 claimed that the effective channel length increases when positive coulombic charge is introduced during irradiation, resulting in a decrease in the short channel effect. Schrankleret al. in 1985 claimed in an experimental study, on the other hand, using 28.0 nm thick gate oxides and 0.9–10 μm channel lengths, that the effect is increased,i.e., the short channel effect begins at longer channel lengths. Wilson and Blue in 1982, in a theoretical study concluded that other than a uniform downward shift in theV _T -channel length curve due to the presence of insulator net fixed positive charge, no effect should be observed. Because of these conflicting reports, it was decided to evaluate this behavior using two different background doping levels inn-channel structures, with physical channel lengths ranging between 1.5 and 10 μm, in 0.1 and 0.5 gWcm (100) Si. To further explore the situation, gate oxide (grown at 1000° C in O₂ containing 4.5% HC1) thicknesses were varied from 17.0–35.0 nm, and the absorbed radiation dose using Al-K_α (1.5 keV) x-rays was varied between 2.4 × 10⁶ rad (SiO₂) and 2.4 × 10⁷ rad (SiO₂). For all conditions studied above, a uniform downward shift in the V_T-Channel length curve was observed, essentially corroborating the theoretical conclusions of Wilson and Blue. In addition to the above, the effects of intentionally doping the gate insulator with boron (1.2 × 10¹² B⁺ cm⁻²) implanted at 8 and 10 keV into 25.0 nm and 31.4 nm oxides, respectively, on short channel effects were evaluated for devices grown onp-type 0.5 Ω.cm substrates. Unlike the devices which did not have excess boron intentionally implanted into the gate insulator, it was found that higher concentrations of boron (2.0 × 10¹⁷ cm⁻³ in the insulator via implantation as compared to 4.2 × 10¹⁶ cm⁻³ incorporated in oxides during the oxide growth on 0.5 Ω.cm type (100) Silicon) leads to smaller short channel effects in unirradiated devices. On the other hand, these heavily doped oxides show a distinct worsening of the short channel effect after exposure to 2.4 × 10⁷ rad (SiO₂) using Al-K_α radiation. Thus, while normal devices exhibit little if any short channel improvement, or degradation following irradiation, intentionally doped insulators show an improvement in short channel characteristics prior to irradiation, and a worsening of the short channel effect following irradiation.     

Personal characteristics and mobile Internet use intensity of consumers with computer-centric communication devices: An exploratory empirical study of iPad and laptop users in Germany

Prior research on adopters of ubiquitous Internet access via cellular radio infrastructures of mobile network operators (MNO) has primarily focused on consumers equipped with enhanced web-enabled phones. In contrast, this work investigates personal characteristics and mobile Internet (MI) use behaviors of consumers who chose computer-centric appliance types for MI access. Two variants of tablet PCs (Apple’s iPad1 and iPad2) and laptops are distinguished as computer-centric communication device categories. Data on two demographic variables, three MNO relationship characteristics and actual MI use intensity (average monthly volume of mobile IP traffic generated by a subscriber in May and June 2011) of 2001 consumers with a flat MI pricing scheme were extracted from customer files of the German subsidiary of a large international MNO. 1371, 367 and 263 of the sample members used an iPad1, an iPad2 and a laptop, respectively for MI access. Compared to the adult population in Germany, persons aged between 17 and 35 years and males are overrepresented among MI adopters with the three studied device types. MI use intensity is highly positively skewed: in each of the three appliance groups, a small number of users disproportionately contributes to the total MI traffic generated by the subjects. MI use intensity is the main variable discriminating between Apple tablet versus laptop MI subscribers. On average, laptop users generate three times more MI traffic than iPad customers. MI use intensity does not differ significantly between iPad1 and iPad2 customers. Age and length of business relationship with the collaborating MNO are the two only studied personal characteristics, which consistently display a significant (negative) association with MI use intensity across the three appliance groups. Conclusions are drawn for MNO on aligning marketing measures to the peculiarities of users with different types of computer-centric MI devices and for scholarly research seeking to enhance the understanding of the influence of various appliance categories on MI adoption and use behaviors.