I started with a ship full of max-level veterans, and I'm just a complete noob.

The old laboratory had two sets of test benches, one connected to germanium transistors and the other to silicon transistors. Metal wires were laid out along the tabletops, and the instrument pointers stopped at different scales. The air was filled with the mixed smell of rosin, metal and old paper.

An elderly German man with gray hair stood beside the blackboard, wearing a dark lab coat with shiny cuffs. He first looked at the notebook in Jiang Ming's hand, then at the two test benches. Without asking his purpose, he picked up the chalk and wrote down a string of numbers.

Germanium has an electron mobility of 3,900.

Silicon, 1,400.

The old man broke the chalk into two pieces and pointed to the line with germanium.

"Looking at this number alone, germanium certainly looks good."

His German, converted from the Tongtianlu dictionary, carried the stern tone commonly found in laboratories.

"However, high-frequency devices are not determined by a single number. Mobility only indicates that the carriers are moving fast, but fast-moving carriers can also be blocked by junction capacitance, surface recombination, and lead inductance."

Jiang Ming opened his notebook, first writing 300 megahertz at the top of the page, then asked, "How should we estimate the single-tube limit for germanium?"

The old man picked up an old test paper, which was covered with cutoff frequency curves at different temperatures. The germanium curve could still rise near room temperature, but it quickly turned downwards as the temperature continued to rise.

"First look at the band gap. Germanium is 0.67 electron volts, while silicon is 1.12 electron volts. The difference lies in the intrinsic carrier concentration."

He wrote the exponential relationship next to the curve with a pencil, and then pushed the temperature from 25 degrees to 70 degrees. The leakage current on the curve rose accordingly, and the instrument pointer formed a black line that stretched to the right on the paper.

"When germanium is heated, the intrinsic carriers increase rapidly, and the leakage current will push the junction operating state away from the design point. The temperature range that the device can withstand is about 70 degrees Celsius."

Jiang Ming stared at the curve, his fingers pressing down on the corner of the paper. The falling curve of the first batch of tubes on the high-frequency test bench appeared in his mind. Although the twenty-seven tubes were concentrated, the leakage current and gain began to drift in different directions as the temperature changed slightly.

"The second limitation is the breakdown voltage."

The old man changed the graph to one showing the junction electric fields of germanium and silicon. The germanium curve touched the breakdown boundary first at a lower voltage, while the usable voltage range of silicon extended much higher.

"With a narrower bandgap, the allowable electric field boundary is lower. The breakdown voltage of germanium devices is only about half that of silicon. If the front-end wants to increase the swing, it often hits this point first."

Jiang Ming wrote the breakdown voltage into his notebook, and also noted down the required gain, noise, and stable operating range for the 24 GHz preamplifier. These three parameters are interdependent; if any one is increased, the other two will become more difficult to achieve.

The old man walked to the germanium transistor test stand, opened an old metal box, and took out several polished germanium wafers, their surfaces gleaming grayish-white under the light.

"The third limitation comes from the surface. The surface states have a greater impact in narrow bandgap materials. Once the surface recombination rate approaches the bulk recombination rate, the minority carrier lifetime will be shortened."

He took out a red pencil and drew dense trap energy levels on the edge of the germanium plate.

"The surface state density you are measuring now is enough to explain part of the frequency loss, but it also changes along with the junction capacitance and base width. Individual repairs can raise the curve, but the whole set of constraints still exists."

Jiang Ming flipped to Xie Xide's photoconductivity spectrum retest data and wrote down the second batch of results from 160 to 180 MHz next to it.

"After we added surface treatment and silicon oxide deposition, the frequency increased by about 20%. The reduction in base width can explain another part, and the remaining part is due to the doping gradient and material parameters."

"This is exactly what engineering data should look like."

The old man put the germanium chip back into the metal box, picked up a sheet of calculation paper, and listed four items on it: transit time, junction capacitance, surface recombination speed, and lead inductance.

"The mobility determines the DC and low-frequency gain, while the high-frequency cutoff frequency depends on the overall response. The thinner the base region, the better, the lower the surface states, the better, and the junction capacitance should also be reduced. If any of these factors remain unchanged, the curve will be dragged down."

He substituted several parameters into the calculation, and the numbers gradually converged on the paper.

"At room temperature, the theoretical ceiling for germanium monofilament is about 500 megahertz, while in engineering it can be stably achieved at 300 to 400 megahertz. Even with perfect technology, it is difficult to exceed 1 gigahertz."

Jiang Ming's hand holding the pen landed on the paper, the pen tip tracing along the line of 500 megahertz, leaving a dark mark on the paper.

"Twenty-four gigahertz pre-class?"

The old man looked up at him, his tone becoming more direct.

"If the target frequency is above one gigahertz, continuing to focus every hour on germanium is like paving stones on a road that is impassable."

The only sound in the laboratory was the slight oscillation of the instrument pointers. Jiang Ming looked down at the calculation paper. The three hundred megahertz that Wang Shouwu had written on the blackboard in 502 was still in his memory. Wu Hanzhang circled the word "germanium" in the preliminary research plan with a pencil, while Fang Xudong put the second batch of data into a folder, waiting for the next test.

He copied all the parameters written down by the old man into a kraft paper notebook, and then redraw the band gaps of germanium and silicon. Silicon has a wider band gap, and the surface oxide layer can form a stable protection. The base region can be further thinned, and the influence of the surface states on the charge carriers decreases accordingly.

"The engineering limits of silicon?"

"Several gigahertz, the specific number depends on the junction capacitance, oxide layer, impurity distribution, and lead structure."

The old man clamped a silicon wafer onto the test bench and gestured for Jiang Ming to observe the changes in the instrument. The current curve maintained a relatively wide operating range as the temperature rose, and the growth rate of surface leakage was much slower than that of germanium.

"Silicon is not easy to work with either. Its melting point, diffusion temperature, and oxide layer formation conditions are more difficult to manage than those of germanium. Its advantage is that it has a path that can be further compressed."

Jiang Ming wrote this sentence down in the margin, turned to the last page, and wrote down a memo comparing the high-frequency performance of germanium and silicon. Below, he listed five items: bandgap, mobility, surface recombination, breakdown voltage, and usable temperature.

The old man looked at his notebook and suddenly asked, "Do you currently have silicon technology on hand?"

"We have experience with diffusion from the Yuanlei-2 project, and the equipment and gas conditions are still being redesigned."

"Then don't take it as a ready-made answer."

The old man put the chalk back in the blackboard slot.

"Switching from germanium to silicon requires changing the material route, redoing the oxide layer, and pushing your existing equipment to a higher level of load at the diffusion temperature. The difficulties in the process will not automatically disappear just because the physical prospects are better."

These words weighed down the forward momentum in Jiang Ming's heart. He originally wanted to include silicon directly in the 24 gigahertz pre-research plan, but then he saw that the equipment in the factory, the purity of the gas, and the temperature zone of the diffusion furnace all required new verification. Changing the route would affect the resource allocation of 502, the Institute of Physics, and the Semiconductor Research Group.

He closed his notebook and nodded to the old man.

"I will let the data establish the conclusion first."

"Once the data is established, the routes will naturally diverge."

The lights in the old laboratory began to shrink outwards. The old man stood between two test benches, his figure cut into two pieces of different brightness by the two band curves on the blackboard. Jiang Ming absorbed the last page of parameters into his mind, and the time limit for psychic communication came to an end.

When he opened his eyes, the clock on the dormitory desk was still standing still, the wind outside the window was blowing the window paper, and an old hardcover memo was pressed on the corner of the desk, with an extra line of numbers written on the edge of the page.

Germanium, theoretically, has a ceiling of about 500 megahertz.

The engineering limit is approximately 300 to 400 megahertz.

Above one gigahertz, the focus shifts to silicon or other devices.

After daybreak, Jiang Ming locked the memo in a safe, made a separate copy of the presentation version, and kept only the carrier transport formula from Qian Xuesen's lecture notes, the mobility data from publicly available literature, and the existing experimental results from the 502 and semiconductor research groups.

In the morning, Fang Xudong brought the second batch of double-diffused germanium triode testers into the office. The cutoff frequencies of the 27 new tubes fell between 160 and 180 MHz, with the best one approaching 180 MHz. The improvement brought about by the surface treatment was clearly visible.

After reviewing the data, Jiang Ming connected the highest point with the median of the first batch and marked a 20% increase between the two curves.

Wu Hanzhang stood by the table, turning the cigarette pack in his hand over and over, but ultimately did not light a cigarette.

"It increased by twenty points."

"It's still far from one gigahertz."

Wu Hanzhang took out the 24 GHz preliminary research plan, turned to the page with the target frequency of the device, and used a pencil to pull down the originally crowded lines, leaving a large blank space.

"When will you reveal your second option?"

"The day I can draw the diagram on the blackboard."

Jiang Ming carefully put away the test sheet.

"Don't use a pen to change the character 'germanium' in the preliminary research plan; use a pencil."

Wu Hanzhang looked at him for a while, then took a pencil from the pen holder and placed it next to the proposal.

In the afternoon, Qian Xuesen's secretary delivered an internal memorandum, requesting the Fifth Academy's guidance group to complete the lateral stability correction simulation scheme before the third demonstration meeting. The Soviet side was expected to provide more complete gyroscope drift data at the beginning of next month.

Jiang Ming drew two timelines on the edge of the memo: one leading to the third guidance demonstration and the other to the joint discussion of devices. The two key nodes would coincide exactly three weeks later.

The remaining time is extremely tight, as the front-stage route needs to be finalized before the guidance system is finalized.

He looked at the two lines, slowly twirled the pencil in his hand, and then pressed the tip heavily in front of the intersection, writing the words "Joint Technical Discussion Meeting".