Dong-chul Kim

Resistance switching characteristics in Li-doped NiO

We investigated the effects of lithium (Li)-doping on bi-stable resistance switching in polycrystalline NiO film in the temperature range of 10 K<T<300 K. Compliance-dependent resistive switching transport revealed some distinctive and interesting features not observed in undoped NiO films previously studied. An analysis of the temperature dependence of the resistive switching transport showed that Li-doping could modify the thermal properties of the off-state leading to a stable on/off switching operation. It is clearly shown that doping Li in NiO can improve NiO’s retention properties and stability of on/off switching voltages.

Analysis and Estimation on EMI Effects in AP-DRAM Interface for a Mobile Platform

Electromagnetic Interference (EMI) is an increasingly important factor in determining whole-system performance of a mobile system. This is driven by size reduction of the mobile platform and the ever-increasing density of electronic components. In this work, we suggest an analysis approach for EMI effects in the interface between an application processor (AP) and dynamic random-access memory (DRAM) by using an I/O driver model including power delivery network (PDN) effects. By applying this approach, the EMI effect by the AP-DRAM interface is able to be accurately estimated when its operating frequency is shifted up/downward depending on the scheme of mobile operations. The EMI effect in the AP-DRAM interface can be characterized by the (1) on-chip metal layout and package layout of the I/O PDN, (2) inserted decoupling capacitance of the I/O PDN, (3) I/O driver properties that define the rising/falling time of signals, and (4) channel properties including crosstalk between adjacent lanes and their frequency response at data transfer. In a time-domain simulation, the extracted I/O driver model was used with extracted AP and memory package models, a channel model, and an interposer. The simulation was carried out by varying input stimulus depending on a bit density ratio, bit length, and a test pattern. As a result, a wide range of spectrum generated by the AP-DRAM interface up to 6 GHz was calculated. The bandwidth of data queue (DQ) signals at the interposer was found to be around 170MHz with multiple harmonics of the fundamental 1.6GHz frequency. In comparison to the measurement, the difference in bandwidth was found to be less than 10MHz and the voltage difference at the harmonics was found to be less than 10dB. Consequently, we proposed an analysis and estimation approach for EMI effects in an AP-DRAM interface which affects the degradation of communication performance in a compact mobile platform and successfully demonstrated its applications for predicting EMI effect in the communication band of interest.

An early-EMI analysis method for the LPDDR interface

In this paper, an accurate noise level estimation technique in the design stage for LPDDR system is presented. In order to predict the system performance, the equivalent circuit based simulation model and the input parameter range for the sweep simulation is required. The package and board are modeled by using RLC equivalent circuits. The input parameter range is determined by investigating the characteristics of the existing products. The noise level of the LPDDR system in the mobile platform can be estimated by using equivalent circuit model and input parameters. It is shown that noise level at the input pad of the receiver using the proposed method has a good agreement with S-Parameter based model within less than 8dB.