Every VLSI interview and exam includes a question that frequently gives many aspirant candidates and students nightmares. The concept of temperature inversion, although a straightforward topic, worries many people. So what precisely is temperature inversion? This article aims to give readers a comprehensive overview of temperature inversion in VLSI.
What Is Temperature Inversion In VLSI?
Temperature inversion is a phenomenon that happens in lower nodes. Because standard cells’ mobility weakens at higher temperatures, the delay of these cells generally increases as the temperature rises. However, in lower technological nodes, the effect of temperature on cell delay is the opposite. In lower nodes, a rise in temperature causes a reduction in the cell’s delay. The impact of temperature on the cell delay is therefore inverted in the lower technology node, and this tendency is known as temperature inversion. The influence of the threshold voltage is predominating over mobility in the lower technology node, which is the fundamental cause of this inversion. Thermal vibrations in the lattice are amplified by temperature increases, which is also the cause of this phenomenon. As a result, electron scattering is enhanced. This can be perceived as an increase in electron collisions, which subtracts from the streamlined flow required for the passage of electrical current. Similar effects occur in semiconductors, and as temperature rises, the mobility of the main carrier diminishes. Both holes and electrons are affected by this.
Also read: Quick Introduction To VLSI Circuits And SystemsHowever, an intriguing effect is seen in semiconductors when a MOS transistor’s supply voltage is lowered. When the temperature rises, the delay via the MOS device falls rather than increases at lower voltages. Since it is generally accepted that mobility reduces with temperature, one could have anticipated a reduction in current and, hence, a reduction in latency. The name “low voltage inverted temperature dependence” is another name for this phenomenon. The amount of time needed to charge or discharge the load capacitance is the cell’s delay. The drain current determines how long the load capacitor takes to charge and discharge. The load capacitor charges and discharges more quickly when the drain current is large, resulting in a shorter delay, and vice versa. Mobility and overdrive voltage are the two main determinants of cell delay variation. The temperature inversion effect is particularly prominent in lower technological nodes when overdrive voltage predominates. To put it simply, when the temperature rises the threshold voltage drops in nodes of lower technology. This results in an increase in drain current and overdrive voltage and a drop in cell delay. Overdrive voltage has taken precedence over the mobility factor in this case. However, overdrive voltage is not as dominant at higher technological nodes, and cell delay fluctuates according to changes in carrier mobility. As a result, the drain current reduces, increasing cell delay.There is still a lot more to learn about temperature inversion and more in VLSI. Curious to learn more about VLSI? Chipedge has got you covered. Chipedge is one of the leading platforms that offer courses to educate you on all the features and analytical tools required for anything from simple to complex circuit designs. Over the years, Chipedge has grown into a suave provider of VLSI courses online. Enlisting in the online VLSI training offered by Chipedge will help you jumpstart your VLSI career. Being the best VLSI Training Institute in Bangalore, Chipedge brings forth an assortment of online VLSI courses. So, if you’re aspiring for a VLSI online course with a certificate, Chipedge is the answer. Get in touch with Chipedge now!Image credits