Hyun-Jung Kim

Abstract This paper explains a systematic way to code qualitative text data to generate causal maps for system dynamics modeling. The study was motivated by the important role qualitative data play in system dynamics and the need for formal methods to document the interpretive process of using text data in modeling. The coding method elucidated in the study was influenced by grounded theory, a flexible, yet rigorous way to build a theory from raw qualitative data. The inductive nature of grounde

In the semiconductor manufacturing industry, the lot size currently tends to be extremely small, even being only 5-8 wafers, whereas conventional lots have 25 identical wafers. The smaller lot size is made because customers demand extremely small lots, and the number of chips in a large 300 mm wafer has increased. Cyclic scheduling is not applicable for such small lot production because the number of identical work cycles accounts for a small proportion of scheduling as compared to the lengths o

Cluster tools, each of which consists of multiple processing modules, one material handling robot, and loadlocks, are widely used for wafer fabrication processes, such as lithography, etching, and deposition. There have been many approaches and algorithms for cyclic scheduling of cluster tools in which the robot repeats a specified sequence for processing identical wafers. However, the lot order size has recently been decreasing due to the larger wafer size and circuit width reductions. In moder

We address a robotic flow shop scheduling problem where two part types are processed on each given set of dedicated machines. A single robot moving on a fixed rail transports one part at a time, and the processing times of the parts vary on the machines within a given time interval. We use a reinforcement learning (RL) approach to obtain efficient robot task sequences to minimise makespan. We model the problem with a Petri net used for a RLenvironment and develop a lower bound for the makespan.

A novel converter topology for high-power battery charger applications is proposed in this paper. The topology adopts the integration structure of two full-bridge converters, which shares one leg of switching device called center-leg. The two full-bridge converters are placed in parallel on the primary side, and are driven in a phase-shift manner. The integrated form of two current-doubler rectifier is adopted on the secondary side, and it has full-bridge structure. With this structure, the prop

Systems approaches present opportunities for public managers and policy makers to view policies and programs in a broader context. This article presents a framework to explain how simulation modeling promotes double‐loop learning in management teams by building and exploring collective mental models as well as by enhancing accuracy of the mental models. The authors discuss the types of problems that may benefit from simulation modeling and illustrate how double‐loop learning occurs in the proces

We examine cyclic scheduling of single-armed and dual-armed cluster tools that concurrently process two wafer types by sharing a process module (PM). Because a PM is shared by two different wafers, the backward and swap sequences, which are prevalently used for single-armed and dual-armed tools without such complexity, respectively, are not effective. We therefore propose new sequences, called alternating backward and alternating swap sequences, for steady cycles of single-armed and dual-armed t

A robotic mobile fulfillment system (RMFS) performs the order fulfillment process by bringing inventory to workers at pick-pack-and-ship warehouses. In the RMFS, robots lift and carry shelving units, called inventory pods, from storage locations to picking stations where workers pick items off the pods and put them into shipping cartons. The robots then return the pods to the storage area and transport other pods. In this article, we consider an item assignment problem in the RMFS in order to ma

1 1. The first author’s current address is the Department of Industrial Engineering and Operations Research, University of California, Berkeley, CA 94720, USA. Modern cluster tools tend to clean the chambers each time a specified number of wafers have been processed. Such cleaning processes are intended to reduce the quality risk due to the residual chemicals within the chambers. When such cleaning processes are introduced, the conventional scheduling methods for cluster tools, such as the swap

An ambipolar channel layer material is required to realize the potential benefits of ambipolar complementary metal-oxide-semiconductor field-effect transistors, namely their compact and efficient nature, reduced reverse power dissipation, and possible applicability to highly integrated circuits. Here, a ternary metal chalcogenide nanocrystal material, FeIn₂S₄, is introduced as a solution-processable ambipolar channel material for field-effect transistors (FETs). The highest

Petri nets are useful for modeling and analyzing complex scheduling problems of automated manufacturing systems, such as robotized cluster tools for semiconductor manufacturing and robot cells with diverse and complex tool architectures and scheduling requirements. While there are many scheduling works on cyclic operation cycles of such systems and their Petri net models, automated manufacturing systems have significant noncyclic operation cycles. For instance, cluster tools cannot repeat identi

We consider a scheduling problem of a robotized cluster tool for semiconductor manufacturing, which should control wafer delays within a chamber so as not to exceed a specified limit under time variation. The prior research has proposed a p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -time event graph, an extension of Petri nets, for modeling the scheduling problem and developed a method of verifying whether a cyclic p <sup xmlns:mml="ht

Cluster tools, which consist of processing modules (PMs) and a transport robot, are used for wafer fabrication processes in semiconductor manufacturing fabs. Once processing of a wafer lot containing several wafers is completed in a tool, an overhead hoist transport (OHT) unloads the lot and transports it to another tool. Since it is not easy to estimate when a wafer lot is completed, an OHT is required to wait for the wafer lot to be completed near the tool, or tools become idle due to the late

This paper examines a parallel machine scheduling problem in which jobs can be processed either in multiple parts or in a complete form and the number of possible job splitting alternatives of jobs is more than one. There are sequence-dependent setup times between different jobs (or parts), and the objective is to minimise makespan by choosing an appropriate processing alternative for each job, assigning parts (or jobs) to machines, and determining the sequence of parts on the machines. This wor

Although post-synthetic anion exchange allows halide perovskite quantum dots to easily change the optical bandgap of materials, additional exchange of shorter ligands is required to use them as active materials in optoelectronic devices. In this study, a novel all-in-one process exchanging ligands and halide anions in film-state for facile color tuning and patterning of cesium lead halide perovskite colloidal quantum dot (PeQD) light-emitting diodes (LEDs) is proposed. The proposed all-in-one pr