Data processing and analytics in L-I-V test of VCSEL

• Main Author: Xu, Zhengyang
• Other Authors: Liu Linbo
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Electrical and electronic engineering
• Online Access: https://hdl.handle.net/10356/145081
• Institution: Nanyang Technological University

L-I-V test is commonly used in semiconductor industry to exam the wafer products’ quality. This test assesses every individual VCSEL (Vertical Cavity Surface Emitting Laser) on the wafer slice with some quantities showing its lasing characteristics when electrically supplied. A software named “LIVCal” is created by C# WinForm (Windows Forms) to conduct all data processing and analytics for the result obtained from a L-I-V test. It includes calculation and graph plotting functions. As the VCSELs are lasing diodes essentially, the L-I-V test is similar to those evaluating diodes’ characteristics. Thus, the test evaluates the VCSEL’s V-I characteristics (voltage-current characteristics), which starts from measuring the voltage V over the VCSEL and the current I passing through the VCSEL when a specific operating current is exerted on the VCSEL. The raw data obtained from the test is passed to “LIVCal”. By “LIVCal”’s calculation, differential resistance Rd and turn-on voltage Vo can be obtained. The VCSEL is also examined with its lasing property such as L-I characteristics (output optical power – operating current characteristics) and intensity-wavelength spectrum. The output optical power is obtained from the calculation with Iph in “LIVCal”, the photocurrent transferred from VCSEL’s laser beam and input into “LIVCal”. Slope efficiency and threshold current can be calculated in “LIVCal” subsequently. Those quantities contribute to the calculations for power conversion efficiency of the VCSEL, which implies the VCSEL’s performance of illuming. The intensity to wavelength spectrum is also examined in “LIVCal” to study the VCSEL’s beam characteristics by comparing to an ideal Gaussian Beam’s property. Thus, both central wavelength and spectral width are evaluated. All calculated quantities are compared with customer’s requirement – whether within its USL (Upper Specification Limit) and LSL (Lower Specification Limit). The product is claimed to be as “pass the test” if the criteria above is fulfilled and “fail the test” if not. As this data processing and analytics method is provided for customer’s reference, 5 sets of sample raw data are going through to assess the method.