From a semiconductor technology perspective, flash memory devices have been around for a very long time; in fact, a Toshiba researcher invented flash memory way back in 1984 and Intel released the first flash chip late in that same decade. Until recently, floating-gate flash memory of one form or another has been the non-volatile memory (NVM) technology of choice for digital cameras, MP3 players, and dozens of other electronic devices. However, the supremacy of flash memory may soon be drawing to a close; technical limitations such as memory wear, speed, power consumption and capacity limitations are spurring memory producers to research new NVM technologies such as phase-change memory (PCM/PRAM), charge trap flash (CTF/SONOS), resistive memory (ReRAM), ferro-electric memory (FeRAM), magneto-resistive memory (MRAM), and others. These new technologies will require R&D labs to re-evaluate their material and device characterization tools and techniques.
Flexible electrical characterization tools are crucial to gaining a better understanding of the physical aspects of any NVM technology. Regardless of the particular memory technology under investigation, pulsing is essential to exercise a cell’s switching behavior. Pulsing with simultaneous measurement provides the data necessary to understand the dynamic behavior of the switching mechanism.
Company executives need to understand that, for those at work in NVM R&D labs, finding an integrated approach to applying pulses to a memory device or material while simultaneously measuring current and voltage has been challenging. In the past, it required integrating a rack of instruments, writing software to coordinate their operation, and accepting various tradeoffs related to cost, performance, and complexity. Creating and maintaining these custom systems typically required an in-house test instrumentation expert with the considerable skills and resources necessary to integrate the various instruments into a working system. Although functional, these “in-house” systems are typically, by necessity, one-off creations with limited test envelopes and cumbersome test controls that require time-consuming data extraction. The measurement approach typically uses a load or sense resistor with an oscilloscope or digitizer to measure the current. Although this is a proven technique, the effect of the load resistor on the voltage delivered to the device has significant downsides for many pulse measurements. Also, correlation across multiple systems and obtaining traceable system-level calibration is effectively impossible.
To stay competitive in NVM design and development, company leadership must be committed to providing the hardware and human resources needed to help their labs to move beyond the limitations that in-house systems impose. Fortunately, a new class of integrated tools offers researchers additional data to gain a better understanding of NVM material and device behavior in less time. For example, Keithley has addressed these needs with the Model 4225-PMU ultra-fast I-V module for the Model 4200-SCS Semiconductor Characterization System, which can measure current and voltage simultaneously at high sampling rates while applying precisely controlled pulses. This approach provides greater insight into the electrical and physical mechanisms that provide the memory behavior. Adding this transient characterization capability to DC characterization provides fundamental data on intrinsic material properties and device response.
For a fast, easy way to learn more about emerging NVM characterization challenges, I’d encourage you to view our free online seminar on Non-Volatile Memory - Characterization and Measurement Techniques.
